SOFTWARE TESTING METHODOLOGIES - NOTES ON SOFTWARE TESTING METHODOLOGIES ... subjected to quality control and testing from component to final stage. ... (Statistical Quality Control).

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    IV B. Tech I semester (JNTUH-R09)


    Assistant Professor

    Ms. K MAYURI

    Assistant Professor





    UNIT- I


    What is testing?

    Testing is the process of exercising or evaluating a system or system components by manual or

    automated means to verify that it satisfies specified requirements.

    The Purpose of Testing

    Testing consumes at least half of the time and work required to produce a functional program.

    o MYTH: Good programmers write code without bugs. (Its wrong!!!)

    o History says that even well written programs still have 1-3 bugs per hundred statements.

    Productivity and Quality in Software:

    o In production of consumer goods and other products, every manufacturing stage is

    subjected to quality control and testing from component to final stage.

    o If flaws are discovered at any stage, the product is either discarded or cycled back for

    rework and correction.

    o Productivity is measured by the sum of the costs of the material, the rework, and the

    discarded components, and the cost of quality assurance and testing.

    o There is a tradeoff between quality assurance costs and manufacturing costs: If sufficient

    time is not spent in quality assurance, the reject rate will be high and so will be the net

    cost. If inspection is good and all errors are caught as they occur, inspection costs will

    dominate, and again the net cost will suffer.

    o Testing and Quality assurance costs for 'manufactured' items can be as low as 2% in

    consumer products or as high as 80% in products such as space-ships, nuclear reactors,

    and aircrafts, where failures threaten life. Whereas the manufacturing cost of software is


    o The biggest part of software cost is the cost of bugs: the cost of detecting them, the cost

    of correcting them, the cost of designing tests that discover them, and the cost of running

    those tests.

    o For software, quality and productivity are indistinguishable because the cost of a

    software copy is trivial.

    o Testing and Test Design are parts of quality assurance should also focus on bug

    prevention. A prevented bug is better than a detected and corrected bug.


    Phases in a tester's mental life:

    Phases in a tester's mental life can be categorized into the following 5 phases:

    1. Phase 0: (Until 1956: Debugging Oriented) There is no difference between testing and debugging. Phase 0 thinking was the norm in early days of software development till testing

    emerged as a discipline.

    2. Phase 1: (1957-1978: Demonstration Oriented) the purpose of testing here is to show that software works. Highlighted during the late 1970s. This failed because the probability of

    showing that software works 'decreases' as testing increases. I.e. the more you test, the more

    likely you will find a bug.

    3. Phase 2: (1979-1982: Destruction Oriented) the purpose of testing is to show that software doesnt work. This also failed because the software will never get released as you

    will find one bug or the other. Also, a bug corrected may also lead to another bug.

    4. Phase 3: (1983-1987: Evaluation Oriented) the purpose of testing is not to prove anything but to reduce the perceived risk of not working to an acceptable value (Statistical Quality

    Control). Notion is that testing does improve the product to the extent that testing catches

    bugs and to the extent that those bugs are fixed. The product is released when the

    confidence on that product is high enough. (Note: This is applied to large software products

    with millions of code and years of use.)

    5. Phase 4: (1988-2000: Prevention Oriented) Testability is the factor considered here. One reason is to reduce the labor of testing. Other reason is to check the testable and non-testable

    code. Testable code has fewer bugs than the code that's hard to test. Identifying the testing

    techniques to test the code is the main key here.

    Test Design:

    We know that the software code must be designed and tested, but many appear to be unaware

    that tests themselves must be designed and tested. Tests should be properly designed and tested

    before applying it to the actual code.

    Testing isnt everything:

    There are approaches other than testing to create better software. Methods other than testing


    1. Inspection Methods: Methods like walkthroughs, desk checking, formal inspections and

    code reading appear to be as effective as testing but the bugs caught dont completely


    2. Design Style: While designing the software itself, adopting stylistic objectives such as

    testability, openness and clarity can do much to prevent bugs.

    3. Static Analysis Methods: Includes formal analysis of source code during compilation. In

    earlier days, it is a routine job of the programmer to do that. Now, the compilers have

    taken over that job.

    4. Languages: The source language can help reduce certain kinds of bugs. Programmers

    find new bugs while using new languages.


    5. Development Methodologies and Development Environment: The development

    process and the environment in which that methodology is embedded can prevent many

    kinds of bugs.


    Testing Versus Debugging: Many people consider both as same. Purpose of testing is to show that a program has

    bugs. The purpose of testing is to find the error or misconception that led to the program's

    failure and to design and implement the program changes that correct the error.

    Debugging usually follows testing, but they differ as to goals, methods and most

    important psychology. The below tab le shows few important differences between testing

    and debugging.

    Testing Debugging

    Testing starts with known conditions,

    uses predefined procedures and has

    predictable outcomes.

    Debugging starts from possibly unknown

    initial conditions and the end cannot be

    predicted except statistically.

    Testing can and should be planned,

    designed and scheduled.

    Procedure and duration of debugging cannot

    be so constrained.

    Testing is a demonstration of error or

    apparent correctness. Debugging is a deductive process.

    Testing proves a programmer's failure. Debugging is the programmer's vindication


    Testing, as executes, should strive to be

    predictable, dull, constrained, rigid and


    Debugging demands intuitive leaps,

    experimentation and freedom.

    Much testing can be done without

    design knowledge.

    Debugging is impossible without detailed

    design knowledge.

    Testing can often be done by an

    outsider. Debugging must be done by an insider.

    Much of test execution and design can

    be automated. Automated debugging is still a dream.

    Function versus Structure:

    o Tests can be designed from a functional or a structural point of view.

    o In Functional testing, the program or system is treated as a black box. It is

    subjected to inputs, and its outputs are verified for conformance to specified

    behavior. Functional testing takes the user point of view- bother about

    functionality and features and not the program's implementation.


    o In Structural testing does look at the implementation details. Things such as

    programming style, control method, source language, database design, and coding

    details dominate structural testing.

    o Both Structural and functional tests are useful, both have limitations, and both

    target different kinds of bugs. Functional tests can detect all bugs but would take

    infinite time to do so. Structural tests are inherently finite but cannot detect all

    errors even if completely executed.

    Designer versus Tester:

    o Test designer is the person who designs the tests where as the tester is the one

    actually tests the code. During functional testing, the designer and tester are

    probably different persons. During unit testing, the tester and the programmer

    merge into one person.

    o Tests designed and executed by the software designers are by nature biased

    towards structural consideration and therefore suffer the limitations of structural


    Modularity versus Efficiency:

    A module is a discrete, well-defined, small component of a system. Smaller the modules,

    difficult to integrate; larger the modules, difficult to understand. Both tests and systems

    can be modular. Testing can and should likewise be organized into modular components.

    Small, independent test cases can be designed to test independent modules.

    Small versus Large:

    Programming in large means constructing programs that consists of many components

    written by many different programmers. Programming in the small is what we do for

    ourselves in the privacy of our own offices. Qualitative and Quantitative changes occur

    with size and so must testing methods and quality criteria.

    Builder versus Buyer:

    Most software is written and used by the same organization. Unfortunately, this situation

    is dishonest because it clouds accountability. If there is no separation between builder and

    buyer, there can be no accountability.

    The different roles / users in a system include:

    1. Builder: Who designs the system and is accountable to the buyer. 2. Buyer: Who pays for the system in the hope of profits from providing services? 3. User: Ultimate beneficiary or victim of the system. The user's interests are also

    guarded by.

    4. Tester: Who is dedicated to the builder's destruction? 5. Operator: Who has to live with the builders' mistakes, the buyers' murky

    (unclear) specifications, testers' oversights and the users' complaints?



    Figure 1.1: A Model for Testing

    Above figure is a model of testing process. It includes three models: A model of the

    environment, a model of the program and a model of the expected bugs.

    Environment: o A Program's environment is the hardware and software required to make it run.

    For online systems, the environment may include communication lines, other

    systems, terminals and operators.

    o The environment also includes all programs that interact with and are used to

    create the program under test - such as OS, linkage editor, loader, compiler, utility


    o Because the hardware and firmware are stable, it is not smart to blame the

    environment for bugs.


    o Most programs are too complicated to understand in detail.

    o The concept of the program is to be simplified in order to test it.

    o If simple model of the program doesnt explain the unexpected behavior, we may

    have to modify that model to include more facts and details. And if that fails, we

    may have to modify the program.


    o Bugs are more insidious (deceiving but harmful) than ever we expect them to be.

    o An unexpected test result may lead us to change our notion of what a bug is and

    our model of bugs.

    o Some optimistic notions that many programmers or testers have about bugs are

    usually unable to test effectively and unable to justify the dirty tests most

    programs need.

    o Optimistic notions about bugs: 1. Benign Bug Hypothesis: The belief that bugs are nice, tame and logical.

    (Benign: Not Dangerous)


    2. Bug Locality Hypothesis: The belief that a bug discovered with in a component affects only that component's behavior.

    3. Control Bug Dominance: The belief those errors in the control structures (if, switch etc) of programs dominate the bugs.

    4. Code / Data Separation: The belief that bugs respect the separation of code and data.

    5. Lingua Salvatore Est.: The belief that the language syntax and semantics (e.g. Structured Coding, Strong typing, etc) eliminates most bugs.

    6. Corrections Abide: The mistaken belief that a corrected bug remains corrected.

    7. Silver Bullets: The mistaken belief that X (Language, Design method, representation, environment) grants immunity from bugs.

    8. Sadism Suffices: The common belief (especially by independent tester) that a sadistic streak, low cunning, and intuition are sufficient to eliminate

    most bugs. Tough bugs need methodology and techniques.

    9. Angelic Testers: The belief that testers are better at test design than programmers is at code design.


    o Tests are formal procedures, Inputs must be prepared, Outcomes should predict,

    tests should be documented, commands need to be executed, and results are to be

    observed. All these errors are subjected to error

    o We do three distinct kinds of testing on a typical software system. They are:

    1. Unit / Component Testing: A Unit is the smallest testable piece of software that can be compiled, assembled, linked, loaded etc. A unit is

    usually the work of one programmer and consists of several hundred or

    fewer lines of code. Unit Testing is the testing we do to show that the unit

    does not satisfy its functional specification or that its implementation

    structure does not match the intended design structure. A Component is

    an integrated aggregate of one or more units. Component Testing is the

    testing we do to show that the component does not satisfy its functional

    specification or that its implementation structure does not match the

    intended design structure.

    2. Integration Testing: Integration is the process by which components are aggregated to create larger components. Integration Testing is testing

    done to show that even though the components were individually

    satisfactory (after passing component testing), checks the combination of

    components are incorrect or inconsistent.

    3. System Testing: A System is a big component. System Testing is aimed at revealing bugs that cannot be attributed to components. It includes

    testing for performance, security, accountability, configuration sensitivity,

    startup and recovery.

    Role of Models: The art of testing consists of creating, selecting, exploring, and revising

    models. Our ability to go through this process depends on the number of different models

    we have at hand and their ability to express a program's behavior.



    Importance of bugs: The importance of bugs depends on frequency, correction cost,

    installation cost, and consequences.

    1. Frequency: How often does that kind of bug occur? Pay more attention to the more frequent bug types.

    2. Correction Cost: What does it cost to correct the bug after it is found? The cost is the sum of 2 factors: (1) the cost of discovery (2) the cost of correction. These

    costs go up dramatically later in the development cycle when the bug is

    discovered. Correction cost also depends on system size.

    3. Installation Cost: Installation cost depends on the number of installations: small for a single user program but more for distributed systems. Fixing one bug and

    distributing the fix could exceed the entire system's development cost.

    4. Consequences: What are the consequences of the bug? Bug consequences can range from mild to catastrophic.

    A reasonable metric for bug importance is

    Importance= ($) = Frequency * (Correction cost + Installation cost + Consequential


    Consequences of bugs: The consequences of a bug can be measure in terms of human

    rather than machine. Some consequences of a bug on a scale of one to ten are:

    1 Mild: The symptoms of the bug offend us aesthetically (gently); a misspelled output or a misaligned printout.

    2 Moderate: Outputs are misleading or redundant. The bug impacts the system's performance.

    3 Annoying: The system's behavior because of the bug is dehumanizing. E.g. Names are truncated or arbitrarily modified.

    4 Disturbing: It refuses to handle legitimate (authorized / legal) transactions. The ATM wont give you money. My credit card is declared invalid.

    5 Serious: It loses track of its transactions. Not just the transaction itself but the fact that the transaction occurred. Accountability is lost.

    6 Very Serious: The bug causes the system to do the wrong transactions. Instead of losing your paycheck, the system credits it to another account or converts deposits

    to withdrawals.

    7 Extreme: The problems aren't limited to a few users or to few transaction types. They are frequent and arbitrary instead of sporadic infrequent) or for unusual


    8 Intolerable: Long term unrecoverable corruption of the database occurs and the corruption is not easily discovered. Serious consideration is given to shutting the

    system down.

    9 Catastrophic: The decision to shut down is taken out of our hands because the system fails.

    10 Infectious: What can be worse than a failed system? One that corrupt other systems even though it does not fall in itself ; that erodes the social physical

    environment; that melts nuclear reactors and starts war.


    Flexible severity rather than absolutes:

    o Quality can be measured as a combination of factors, of which number of bugs

    and their severity is only one component.

    o Many organizations have designed and used satisfactory, quantitative, quality


    o Because bugs and their symptoms play a significant role in such metrics, as

    testing progresses, you see the quality rise to a reasonable value which is deemed

    to be safe to ship the product.

    o The factors involved in bug severity are:

    1. Correction Cost: Not so important because catastrophic bugs may be corrected easier and small bugs may take major time to debug.

    2. Context and Application Dependency: Severity depends on the context and the application in which it is used.

    3. Creating Culture Dependency: Whats important depends on the creators of software and their cultural aspirations. Test tool vendors are

    more sensitive about bugs in their software then games software vendors.

    4. User Culture Dependency: Severity also depends on user culture. Naive users of PC software go crazy over bugs where as pros (experts) may just


    5. The software development phase: Severity depends on development phase. Any bugs gets more severe as it gets closer to field use and more

    severe the longer it has been around.


    There is no universally correct way categorize bugs. The taxonomy is not rigid.

    A given bug can be put into one or another category depending on its history and the

    programmer's state of mind.

    The major categories are: (1) Requirements, Features and Functionality Bugs (2)

    Structural Bugs (3) Data Bugs (4) Coding Bugs (5) Interface, Integration and System

    Bugs (6) Test and Test Design Bugs.

    Requirements, Features and Functionality Bugs: Various categories in Requirements, Features and Functionality bugs include:

    1. Requirements and Specifications Bugs:

    Requirements and specifications developed from them can be incomplete ambiguous, or self-contradictory. They can be misunderstood or impossible to understand.

    The specifications that don't have flaws in them may change while the design is in progress. The features are added, modified and deleted.

    Requirements, especially, as expressed in specifications are a major source of expensive bugs.

    The range is from a few percentages to more than 50%, depending on the application and environment.

    What hurts most about the bugs is that they are the earliest to invade the system and the last to leave.


    2. Feature Bugs:

    Specification problems usually create corresponding feature problems.

    A feature can be wrong, missing, or superfluous (serving no useful purpose). A missing feature or case is easier to detect and correct. A wrong feature could have deep design


    Removing the features might complicate the software, consume more resources, and foster more bugs.

    3. Feature Interaction Bugs:

    Providing correct, clear, implementable and testable feature specifications is not enough.

    Features usually come in groups or related features. The features of each group and the interaction of features within the group are usually well tested.

    The problem is unpredictable interactions between feature groups or even between individual features. For example, your telephone is provided with call holding and call

    forwarding. The interactions between these two features may have bugs.

    Every application has its peculiar set of features and a much bigger set of unspecified feature interaction potentials and therefore result in feature interaction bugs.

    Specification and Feature Bug Remedies:

    Most feature bugs are rooted in human to human communication problems. One solution is to use high-level, formal specification languages or systems.

    Such languages and systems provide short term support but in the long run, does not solve the problem.

    Short term Support: Specification languages facilitate formalization of requirements and inconsistency and ambiguity analysis.

    Long term Support: Assume that we have a great specification language and that can be used to create unambiguous, complete specifications with unambiguous complete tests

    and consistent test criteria.

    The specification problem has been shifted to a higher level but not eliminated. Testing Techniques for functional bugs: Most functional test techniques- that is

    those techniques which are based on a behavioral description of software, such as

    transaction flow testing, syntax testing, domain testing, logic testing and state

    testing are useful in testing functional bugs.

    Structural bugs: Various categories in Structural bugs include: 1. Control and Sequence Bugs:

    Control and sequence bugs include paths left out, unreachable code, improper nesting of loops, loop-back or loop termination criteria incorrect, missing process steps, duplicated

    processing, unnecessary processing, rampaging, GOTO's, ill-conceived (not properly

    planned) switches, spaghetti code, and worst of all, pachinko code.

    One reason for control flow bugs is that this area is amenable (supportive) to theoretical treatment.

    Most of the control flow bugs are easily tested and caught in unit testing.

    Another reason for control flow bugs is that use of old code especially ALP & COBOL code are dominated by control flow bugs.


    Control and sequence bugs at all levels are caught by testing, especially structural testing, more specifically path testing combined with a bottom line functional test based on a


    2. Logic Bugs:

    Bugs in logic, especially those related to misunderstanding how case statements and logic operators behave singly and combinations

    Also includes evaluation of boolean expressions in deeply nested IF-THEN-ELSE constructs.

    If the bugs are parts of logical (i.e. boolean) processing not related to control flow, they are characterized as processing bugs.

    If the bugs are parts of a logical expression (i.e. control-flow statement) which is used to direct the control flow, then they are categorized as control-flow bugs.

    3. Processing Bugs:

    Processing bugs include arithmetic bugs, algebraic, mathematical function evaluation, algorithm selection and general processing.

    Examples of Processing bugs include: Incorrect conversion from one data representation to other, ignoring overflow, improper use of greater-than-or-equal etc

    Although these bugs are frequent (12%), they tend to be caught in good unit testing.

    4. Initialization Bugs:

    Initialization bugs are common. Initialization bugs can be improper and superfluous.

    Superfluous bugs are generally less harmful but can affect performance.

    Typical initialization bugs include: Forgetting to initialize the variables before first use, assuming that they are initialized elsewhere, initializing to the wrong format,

    representation or type etc

    Explicit declaration of all variables, as in Pascal, can reduce some initialization problems.

    5. Data-Flow Bugs and Anomalies:

    Most initialization bugs are special case of data flow anomalies.

    A data flow anomaly occurs where there is a path along which we expect to do something unreasonable with data, such as using an uninitialized variable, attempting to use a

    variable before it exists, modifying and then not storing or using the result, or initializing

    twice without an intermediate use.

    Data bugs:

    Data bugs include all bugs that arise from the specification of data objects, their formats, the number of such objects, and their initial values.

    Data Bugs are at least as common as bugs in code, but they are often treated as if they did not exist at all.

    Code migrates data: Software is evolving towards programs in which more and more of the control and processing functions are stored in tables.

    Because of this, there is an increasing awareness that bugs in code are only half the battle and the data problems should be given equal attention.


    Dynamic Data Vs Static data:

    Dynamic data are transitory. Whatever their purpose their lifetime is relatively short, typically the processing time of one transaction. A storage object may be used to hold

    dynamic data of different types, with different formats, attributes and residues.

    Dynamic data bugs are due to leftover garbage in a shared resource. This can be handled in one of the three ways: (1) Clean up after the use by the user (2) Common Cleanup by

    the resource manager (3) No Clean up

    Static Data are fixed in form and content. They appear in the source code or database directly or indirectly, for example a number, a string of characters, or a bit pattern.

    Compile time processing will solve the bugs caused by static data.

    Information, parameter, and control:

    Static or dynamic data can serve in one of three roles, or in combination of roles: as a parameter,

    for control, or for information.

    Content, Structure and Attributes:

    Content can be an actual bit pattern, character string, or number put into a data structure. Content is a pure bit pattern and has no meaning unless it is interpreted by a hardware or

    software processor. All data bugs result in the corruption or misinterpretation of content.

    Structure relates to the size, shape and numbers that describe the data object, which is memory location used to store the content. (E.g. A two dimensional array).

    Attributes relates to the specification meaning that is the semantics associated with the contents of a data object. (E.g. an integer, an alphanumeric string, a subroutine). The

    severity and subtlety of bugs increases as we go from content to attributes because the

    things get less formal in that direction.

    Coding bugs:

    Coding errors of all kinds can create any of the other kind of bugs.

    Syntax errors are generally not important in the scheme of things if the source language translator has adequate syntax checking.

    If a program has many syntax errors, then we should expect many logic and coding bugs.

    The documentation bugs are also considered as coding bugs which may mislead the maintenance programmers.

    Interface, integration, and system bugs: Various categories of bugs in Interface, Integration, and System Bugs are:

    1. External Interfaces:

    The external interfaces are the means used to communicate with the world.

    These include devices, actuators, sensors, input terminals, printers, and communication lines.

    The primary design criterion for an interface with outside world should be robustness.


    All external interfaces, human or machine should employ a protocol. The protocol may be wrong or incorrectly implemented.

    Other external interface bugs are: invalid timing or sequence assumptions related to external signals

    Misunderstanding external input or output formats.

    Insufficient tolerance to bad input data.

    2. Internal Interfaces:

    Internal interfaces are in principle not different from external interfaces but they are more controlled.

    A best example for internal interfaces is communicating routines.

    The external environment is fixed and the system must adapt to it but the internal environment, which consists of interfaces with other components, can be negotiated.

    Internal interfaces have the same problem as external interfaces.

    3. Hardware Architecture:

    Bugs related to hardware architecture originate mostly from misunderstanding how the hardware works.

    Examples of hardware architecture bugs: address generation error, i/o device operation / instruction error, waiting too long for a response, incorrect interrupt handling etc.

    The remedy for hardware architecture and interface problems is twofold: (1) Good Programming and Testing (2) Centralization of hardware interface software in programs

    written by hardware interface specialists.

    4. Operating System Bugs:

    Program bugs related to the operating system are a combination of hardware architecture and interface bugs mostly caused by a misunderstanding of what it is the operating

    system does.

    Use operating system interface specialists, and use explicit interface modules or macros for all operating system calls.

    This approach may not eliminate the bugs but at least will localize them and make testing easier.

    5. Software Architecture:

    Software architecture bugs are the kind that called - interactive.

    Routines can pass unit and integration testing without revealing such bugs.

    Many of them depend on load, and their symptoms emerge only when the system is stressed.

    Sample for such bugs: Assumption that there will be no interrupts, Failure to block or un block interrupts, Assumption that memory and registers were initialized or not initialized


    Careful integration of modules and subjecting the final system to a stress test are effective methods for these bugs.


    6. Control and Sequence Bugs (Systems Level):

    These bugs include: Ignored timing, Assuming that events occur in a specified sequence,

    Working on data before all the data have arrived from disc, Waiting for an impossible

    combination of prerequisites, Missing, wrong, redundant or superfluous process steps.

    The remedy for these bugs is highly structured sequence control.

    Specialize, internal, sequence control mechanisms are helpful.

    7. Resource Management Problems:

    Memory is subdivided into dynamically allocated resources such as buffer blocks, queue blocks, task control blocks, and overlay buffers.

    External mass storage units such as discs, are subdivided into memory resource pools.

    Some resource management and usage bugs: Required resource not obtained, Wrong resource used, Resource is already in use, Resource dead lock etc

    Resource Management Remedies: A design remedy that prevents bugs is always preferable to a test method that discovers them.

    The design remedy in resource management is to keep the resource structure simple: the fewest different kinds of resources, the fewest pools, and no private resource


    8. Integration Bugs:

    Integration bugs are bugs having to do with the integration of, and with the interfaces between, working and tested components.

    These bugs results from inconsistencies or incompatibilities between components.

    The communication methods include data structures, call sequences, registers, semaphores, and communication links and protocols results in integration bugs.

    The integration bugs do not constitute a big bug category (9%) they are expensive category because they are usually caught late in the game and because they force changes

    in several components and/or data structures.

    9. System Bugs:

    System bugs covering all kinds of bugs that cannot be ascribed to a component or to their simple interactions, but result from the totality of interactions between many components

    such as programs, data, hardware, and the operating systems.

    There can be no meaningful system testing until there has been thorough component and integration testing.

    System bugs are infrequent (1.7%) but very important because they are often found only after the system has been fielded.


    Testing: testers have no immunity to bugs. Tests require complicated scenarios and databases.

    They require code or the equivalent to execute and consequently they can have bugs.

    Test criteria: if the specification is correct, it is correctly interpreted and implemented, and a proper test has been designed; but the criterion by which the software's behavior is


    judged may be incorrect or impossible. So, a proper test criteria has to be designed. The

    more complicated the criteria, the likelier they are to have bugs.

    Remedies: The remedies of test bugs are:

    1. Test Debugging: The first remedy for test bugs is testing and debugging the tests. Test

    debugging, when compared to program debugging, is easier because tests, when properly

    designed are simpler than programs and do not have to make concessions to efficiency.

    2. Test Quality Assurance: Programmers have the right to ask how quality in independent

    testing is monitored.

    3. Test Execution Automation: The history of software bug removal and prevention is

    indistinguishable from the history of programming automation aids. Assemblers, loaders,

    compilers are developed to reduce the incidence of programming and operation errors. Test

    execution bugs are virtually eliminated by various test execution automation tools.

    4. Test Design Automation: Just as much of software development has been automated, much

    test design can be and has been automated. For a given productivity rate, automation reduces the

    bug count - be it for software or be it for tests.



    Path Testing:

    o Path Testing is the name given to a family of test techniques based on judiciously

    selecting a set of test paths through the program.

    o If the set of paths are properly chosen then we have achieved some measure of

    test thoroughness. For example, pick enough paths to assure that every source

    statement has been executed at least once.

    o Path testing techniques are the oldest of all structural test techniques.

    o Path testing is most applicable to new software for unit testing. It is a structural


    o It requires complete knowledge of the program's structure.

    o It is most often used by programmers to unit test their own code.

    o The effectiveness of path testing rapidly deteriorates as the size of the software

    aggregate under test increases.

    The Bug Assumption:

    o The bug assumption for the path testing strategies is that something has gone

    wrong with the software that makes it take a different path than intended.

    o As an example "GOTO X" where "GOTO Y" had been intended.

    o Structured programming languages prevent many of the bugs targeted by path

    testing: as a consequence the effectiveness for path testing for these languages is

    reduced and for old code in COBOL, ALP, FORTRAN and Basic, the path testing

    is indispensable.


    Control Flow Graphs:

    o The control flow graph is a graphical representation of a program's control

    structure. It uses the elements named process blocks, decisions, and junctions.

    o The flow graph is similar to the earlier flowchart, with which it is not to be


    o Flow Graph Elements: A flow graph contains four different types of elements.

    (1) Process Block (2) Decisions (3) Junctions (4) Case Statements

    1. Process Block: A process block is a sequence of program statements uninterrupted

    by either decisions or junctions.

    It is a sequence of statements such that if any one of statement of

    the block is executed, then all statement thereof are executed.

    Formally, a process block is a piece of straight line code of one

    statement or hundreds of statements.

    A process has one entry and one exit. It can consists of a single

    statement or instruction, a sequence of statements or instructions, a

    single entry/exit subroutine, a macro or function call, or a sequence

    of these.

    2. Decisions: A decision is a program point at which the control flow can


    Machine language conditional branch and conditional skip

    instructions are examples of decisions.

    Most of the decisions are two-way but some are three way

    branches in control flow.

    3. Case Statements: A case statement is a multi-way branch or decisions.

    Examples of case statement are a jump table in assembly language,

    and the PASCAL case statement.

    From the point of view of test design, there are no differences

    between Decisions and Case Statements

    4. Junctions: A junction is a point in the program where the control flow can


    Examples of junctions are: the target of a jump or skip instruction

    in ALP, a label that is a target of GOTO.


    Figure 2.1: Flow graph Elements

    Control Flow Graphs Vs Flowcharts: o A program's flow chart resembles a control flow graph.

    o In flow graphs, we don't show the details of what is in a process block.

    o In flow charts every part of the process block is drawn.

    o The flowchart focuses on process steps, where as the flow graph focuses on control flow

    of the program.

    o The act of drawing a control flow graph is a useful tool that can help us clarify the control

    flow and data flow issues.

    Notational Evolution: The control flow graph is simplified representation of the program's structure.The notation

    changes made in creation of control flow graphs:

    o The process boxes weren't really needed. There is an implied process on every line

    joining junctions and decisions.

    o We don't need to know the specifics of the decisions, just the fact that there is a branch.

    o The specific target label names aren't important-just the fact that they exist. So we can

    replace them by simple numbers.

    o To understand this, we will go through an example (Figure 2.2) written in a FORTRAN

    like programming language called Programming Design Language (PDL). The

    program's corresponding flowchart (Figure 2.3) and flowgraph (Figure 2.4) were also

    provided below for better understanding.


    o The first step in translating the program to a flowchart is shown in Figure 2.3, where we

    have the typical one-for-one classical flowchart. Note that complexity has increased,

    clarity has decreased, and that we had to add auxiliary labels (LOOP, XX, and YY),

    which have no actual program counterpart. In Figure 2.4 we merged the process steps and

    replaced them with the single process box.

    o We now have a control flow graph. But this representation is still too busy. We simplify

    the notation further to achieve Figure 2.5, where for the first time we can really see what

    the control flow looks like.

    Figure 2.2: Program Example (PDL)

    Figure 2.3: One-to-one flowchart for example program in Figure 2.2


    Figure 2.4: Control Flow graph for example in Figure 2.2

    Figure 2.5: Simplified Flow graph Notation

    Figure 2.6: Even Simplified Flow graph Notation

    The final transformation is shown in Figure 2.6, where we've dropped the node numbers to

    achieve an even simpler representation. The way to work with control flow graphs is to use the

    simplest possible representation - that is, no more information than you need to correlate back to

    the source program or PDL.



    Although graphical representations of flow graphs are revealing, the details of the control flow

    inside a program they are often inconvenient.

    In linked list representation, each node has a name and there is an entry on the list for each link

    in the flow graph. Only the information pertinent to the control flow is shown.

    Linked List representation of Flow Graph:

    Figure 2.7: Linked List Control Flow graph Notation


    A flow graph is a pictorial representation of a program and not the program itself, just as a

    topographic map.

    You cant always associate the parts of a program in a unique way with flow graph parts because

    many program structures, such as if-then-else constructs, consists of a combination of decisions,

    junctions, and processes.

    The translation from a flow graph element to a statement and vice versa is not always unique.

    (See Figure 2.8)


    Figure 2.8: Alternative Flow graphs for same logic

    (Statement "IF (A=0) AND (B=1) THEN . . .").

    An improper translation from flow graph to code during coding can lead to bugs, and improper

    translation during the test design lead to missing test cases and causes undiscovered bugs.


    Flowcharts can be

    1. Handwritten by the programmer. 2. Automatically produced by a flowcharting program based on a mechanical analysis of

    the source code.

    3. Semi automatically produced by a flow charting program based in part on structural analysis of the source code and in part on directions given by the programmer.

    There are relatively few control flow graph generators.


    Path: A path through a program is a sequence of instructions or statements that starts at

    an entry, junction, or decision and ends at another, or possibly the same junction,

    decision, or exit.

    o A path may go through several junctions, processes, or decisions, one or more


    o Paths consist of segments.

    o The segment is a link - a single process that lies between two nodes.

    o A path segment is succession of consecutive links that belongs to some path.

    o The length of path measured by the number of links in it and not by the number of

    the instructions or statements executed along that path.

    o The name of a path is the name of the nodes along the path.



    There are many paths between the entry and exit of a typical routine.

    Every decision doubles the number of potential paths. And every loop multiplies the number of

    potential paths by the number of different iteration values possible for the loop.

    Defining complete testing:

    1. Exercise every path from entry to exit. 2. Exercise every statement or instruction at least once. 3. Exercise every branch and case statement, in each direction at least once.

    If prescription 1 is followed then 2 and 3 are automatically followed. But it is impractical for

    most routines. It can be done for the routines that have no loops, in which it is equivalent to 2

    and 3 prescriptions.

    EXAMPLE: Here is the correct version.

    For X negative, the output is X + A, while for X greater than or equal to zero, the output is X +

    2A. Following prescription 2 and executing every statement, but not every branch, would not

    reveal the bug in the following incorrect version:

    A negative value produces the correct answer. Every statement can be executed, but if the test

    cases do not force each branch to be taken, the bug can remain hidden. The next example uses a

    test based on executing each branch but does not force the execution of all statements:

    The hidden loop around label 100 is not revealed by tests based on prescription 3 alone because

    no test forces the execution of statement 100 and the following GOTO statement. Furthermore,

    label 100 is not flagged by the compiler as an unreferenced label and the subsequent GOTO does

    not refer to an undefined label.

    A Static Analysis (that is, an analysis based on examining the source code or structure) cannot

    determine whether a piece of code is or is not reachable. There could be subroutine calls with


    parameters that are subroutine labels, or in the above example there could be a GOTO that

    targeted label 100 but could never achieve a value that would send the program to that label.

    Only a Dynamic Analysis (that is, an analysis based on the code's behavior while running -

    which is to say, to all intents and purposes, testing) can determine whether code is reachable or

    not and therefore distinguish between the ideal structure we think we have and the actual, buggy



    Any testing strategy based on paths must at least both exercise every instruction and take

    branches in all directions.

    A set of tests that does this is not complete in an absolute sense, but it is complete in the sense

    that anything less must leave something untested.

    So we have explored three different testing criteria or strategies out of a potentially infinite

    family of strategies.

    i. Path Testing (Pinf): 1. Execute all possible control flow paths through the program: typically, this is

    restricted to all possible entry/exit paths through the program.

    2. If we achieve this prescription, we are said to have achieved 100% path coverage. This is the strongest criterion in the path testing strategy family: it is generally

    impossible to achieve.

    ii. Statement Testing (P1): 1. Execute all statements in the program at least once under some test. If we do enough

    tests to achieve this, we are said to have achieved 100% statement coverage.

    2. An alternate equivalent characterization is to say that we have achieved 100% node coverage. We denote this by C1.

    3. This is the weakest criterion in the family: testing less than this for new software is unconscionable (unprincipled or cannot be accepted) and should be criminalized.

    iii. Branch Testing (P2): 1. Execute enough tests to assure that every branch alternative has been exercised at least

    once under some test.

    2. If we do enough tests to achieve this prescription, then we have achieved 100% branch coverage.

    3. An alternative characterization is to say that we have achieved 100% link coverage. 4. For structured software, branch testing and therefore branch coverage strictly includes

    statement coverage.

    5. We denote branch coverage by C2.

    Commonsense and Strategies:

    Branch and statement coverage are accepted today as the minimum mandatory testing



    The question "why not use a judicious sampling of paths?, what is wrong with leaving

    some code, untested?" is ineffectual in the view of common sense and experience since:

    (1.) Not testing a piece of a code leaves a residue of bugs in the program in proportion to

    the size of the untested code and the probability of bugs. (2.) The high probability paths

    are always thoroughly tested if only to demonstrate that the system works properly.

    Which paths to be tested? You must pick enough paths to achieve C1+C2. The question

    of what is the fewest number of such paths is interesting to the designer of test tools that

    help automate the path testing, but it is not crucial to the pragmatic (practical) design of

    tests. It is better to make many simple paths than a few complicated paths.

    Path Selection Example:

    Figure 2.9: An example flow graph to explain path selection

    Practical Suggestions in Path Testing:

    1. Draw the control flow graph on a single sheet of paper.

    2. Make several copies - as many as you will need for coverage (C1+C2) and several more.

    3. Use a yellow highlighting marker to trace paths. Copy the paths onto master sheets.

    4. Continue tracing paths until all lines on the master sheet are covered, indicating that you

    appear to have achieved C1+C2.

    5. As you trace the paths, create a table that shows the paths, the coverage status of each

    process, and each decision.

    6. The above paths lead to the following table considering Figure 2.9:


    7. After you have traced a covering path set on the master sheet and filled in the table for

    every path, check the following:

    1. Does every decision have a YES and a NO in its column? (C2) 2. Has every case of all case statements been marked? (C2) 3. Is every three - way branch (less, equal, greater) covered? (C2) 4. Is every link (process) covered at least once? (C1)

    8. Revised Path Selection Rules:

    Pick the simplest, functionally sensible entry/exit path.

    Pick additional paths as small variation from previous paths. Pick paths that do not have

    loops rather than paths that do. Favor short paths that make sense over paths that don't.

    Pick additional paths that have no obvious functional meaning only if it's necessary to

    provide coverage.

    Be comfortable with your chosen paths. Play your hunches (guesses) and give your

    intuition free reign as long as you achieve C1+C2.

    Don't follow rules slavishly (blindly) - except for coverage.


    Cases for a single loop: A Single loop can be covered with two cases: Looping and Not looping.

    But, experience shows that many loop-related bugs are not discovered by C1+C2. Bugs hide

    themselves in corners and congregate at boundaries - in the cases of loops, at or around the

    minimum or maximum number of times the loop can be iterated. The minimum number of

    iterations is often zero, but it need not be.

    CASE 1: Single loop, Zero minimum, N maximum, No excluded values 1. Try bypassing the loop (zero iterations). If you can't, you either have a bug, or zero is not

    the minimum and you have the wrong case.

    2. Could the loop-control variable be negative? Could it appear to specify a negative number

    of iterations? What happens to such a value?

    3. One pass through the loop.

    4. Two passes through the loop.

    5. A typical number of iterations, unless covered by a previous test.

    6. One less than the maximum number of iterations.

    7. The maximum number of iterations.


    8. Attempt one more than the maximum number of iterations. What prevents the loop-control

    variable from having this value? What will happen with this value if it is forced?

    CASE 2: Single loop, Non-zero minimum, No excluded values 1. Try one less than the expected minimum. What happens if the loop control variable's value

    is less than the minimum? What prevents the value from being less than the minimum?

    2. The minimum number of iterations.

    3. One more than the minimum number of iterations.

    4. Once, unless covered by a previous test.

    5. Twice, unless covered by a previous test.

    6. A typical value.

    7. One less than the maximum value.

    8. The maximum number of iterations.

    9. Attempt one more than the maximum number of iterations.

    CASE 3: Single loops with excluded values

    Treat single loops with excluded values as two sets of tests consisting of loops without

    excluded values, such as case 1 and 2 above.

    Example, the total range of the loop control variable was 1 to 20, but that values 7, 8,9,10

    were excluded. The two sets of tests are 1-6 and 11-20.

    The test cases to attempt would be 0,1,2,4,6,7 for the first range and 10,11,15,19,20,21 for

    the second range.

    Kinds of Loops: There are only three kinds of loops with respect to path testing:

    Nested Loops:

    The number of tests to be performed on nested loops will be the exponent of the tests

    performed on single loops.As we cannot always afford to test all combinations of nested

    loops' iterations values. Here's a tactic used to discard some of these values:

    1. Start at the inner most loop. Set all the outer loops to their minimum values. 2. Test the minimum, minimum+1, typical, maximum-1 , and maximum for the innermost loop, while holding the outer loops at their minimum iteration parameter values. Expand

    the tests as required for out of range and excluded values.

    3. If you've done the outmost loop, GOTO step 5, else move out one loop and set it up as in step 2 with all other loops set to typical values.

    4. Continue outward in this manner until all loops have been covered. 5. Do all the cases for all loops in the nest simultaneously.

    Concatenated Loops: Concatenated loops fall between single and nested loops with respect to test cases. Two

    loops are concatenated if it's possible to reach one after exiting the other while still on a

    path from entrance to exit.

    If the loops cannot be on the same path, then they are not concatenated and can be treated

    as individual loops.


    Horrible Loops: A horrible loop is a combination of nested loops, the use of code that jumps into and out of

    loops, intersecting loops, hidden loops, and cross connected loops.

    Makes iteration value selection for test cases an awesome and ugly task, which is another

    reason such structures should be avoided.

    Figure 2.10: Example of Loop types

    Loop Testing Time: Any kind of loop can lead to long testing time, especially if all the extreme value cases are

    to attempted (Max-1, Max, Max+1).


    This situation is obviously worse for nested and dependent concatenated loops.

    Consider nested loops in which testing the combination of extreme values lead to long test

    times. Several options to deal with:

    Prove that the combined extreme cases are hypothetically possible, they are not possible in

    the real world

    Put in limits or checks that prevent the combined extreme cases. Then you have to test the

    software that implements such safety measures.


    PREDICATE: The logical function evaluated at a decision is called Predicate. The direction

    taken at a decision depends on the value of decision variable. Some examples are: A>0,


    PATH PREDICATE: A predicate associated with a path is called a Path Predicate. For

    example, "x is greater than zero", "x+y>=90", "w is either negative or equal to 10 is true" is a

    sequence of predicates whose truth values will cause the routine to take a specific path.


    The path taken through a multiway branch such as a computed GOTO's, case statement, or

    jump tables cannot be directly expressed in TRUE/FALSE terms.

    Although, it is possible to describe such alternatives by using multi valued logic, an

    expedient (practical approach) is to express multiway branches as an equivalent set of

    if..then..else statements.

    For example a three way case statement can be written as: If case=1 DO A1 ELSE (IF


    INPUTS: In testing, the word input is not restricted to direct inputs, such as variables in a subroutine

    call, but includes all data objects referenced by the routine whose values are fixed prior to

    entering it.

    For example, inputs in a calling sequence, objects in a data structure, values left in registers,

    or any combination of object types.

    The input for a particular test is mapped as a one dimensional array called as an Input



    The simplest predicate depends only on input variables.

    For example if x1,x2 are inputs, the predicate might be x1+x2>=7, given the values of x1

    and x2 the direction taken through the decision is based on the predicate is determined at

    input time and does not depend on processing.

    Another example, assume a predicate x1+y>=0 that along a path prior to reaching this

    predicate we had the assignment statement y=x2+7. although our predicate depends on

    processing, we can substitute the symbolic expression for y to obtain an equivalent predicate



    The act of symbolic substitution of operations along the path in order to express the

    predicate solely in terms of the input vector is called predicate interpretation.

    Sometimes the interpretation may depend on the path; for example,


    ON X GOTO A, B, C, ...

    A: Z := 7 @ GOTO HEM

    B: Z := -7 @ GOTO HEM

    C: Z := 0 @ GOTO HEM





    The predicate interpretation at HEN depends on the path we took through the first multiway

    branch. It yields for the three cases respectively, if Y+7>0, Y-7>0, Y>0.

    The path predicates are the specific form of the predicates of the decisions along the selected

    path after interpretation.


    The path predicates take on truth values based on the values of input variables, either

    directly or indirectly.

    If a variable's value does not change as a result of processing, that variable is independent

    of the processing.

    If the variable's value can change as a result of the processing, the variable is process


    A predicate whose truth value can change as a result of the processing is said to be process

    dependent and one whose truth value does not change as a result of the processing is

    process independent. Process dependence of a predicate does not always follow from dependence of the input

    variables on which that predicate is based.

    CORRELATION OF VARIABLES AND PREDICATES: Two variables are correlated if every combination of their values cannot be independently


    Variables whose values can be specified independently without restriction are called


    A pair of predicates whose outcomes depend on one or more variables in common are said to

    be correlated predicates.

    For example, the predicate X==Y is followed by another predicate X+Y == 8. If we select X

    and Y values to satisfy the first predicate, we might have forced the 2nd predicate's truth value

    to change.

    Every path through a routine is achievable only if all the predicates in that routine are uncorrelated.


    A path predicate expression is a set of boolean expressions, all of which must be satisfied to

    achieve the selected path.






    Any set of input values that satisfy all of the conditions of the path predicate expression will

    force the routine to the path.

    Sometimes a predicate can have an OR in it.


    A: X5 > 0

    B: X1 + 3X2 + 17

    >= 0

    C: X3 = 17

    D: X4 - X1 >=


    E: X6 < 0

    B: X1 + 3X2 + 17

    >= 0

    C: X3 = 17

    D: X4 - X1 >=


    Boolean algebra notation to denote the boolean expression:



    Compound Predicate: Predicates of the form A OR B, A AND B and more complicated

    Boolean expressions are called as compound predicates.

    Sometimes even a simple predicate becomes compound after interpretation. Example: the

    predicate if (x=17) whose opposite branch is if x.NE.17 which is equivalent to x>17. Or.

    X 0

    then ...

    X = 7


    if X+Y > 0

    then ...


    o If the test case sets Y=1 the desired path is taken in either case, but there is still a bug.

    Equality Blindness: o Equality blindness occurs when the path selected by a prior predicate results in a value that

    works both for the correct and buggy predicate.

    o For Example:

    Correct Buggy

    if Y = 2 then


    if X+Y > 3

    then ...

    if Y = 2 then


    if X > 1

    then ...

    o The first predicate if y=2 forces the rest of the path, so that for any positive value of x. the path taken at the second predicate will be the same for the correct and buggy version.

    Self Blindness: o Self blindness occurs when the buggy predicate is a multiple of the correct predicate and as

    a result is indistinguishable along that path.

    o For Example:

    Correct Buggy

    X = A


    if X-1 > 0

    then ...

    X = A


    if X+A-2 > 0

    then ...

    1. The assignment (x=a) makes the predicates multiples of each other, so the direction taken is the same for the correct and buggy version.


    o Review: achievable and unachievable paths: 1. We want to select and test enough paths to achieve a satisfactory notion of test completeness

    such as C1+C2.

    2. Extract the programs control flow graph and select a set of tentative covering paths. 3. For any path in that set, interpret the predicates along the path as needed to express them in

    terms of the input vector. In general individual predicates are compound or may become

    compound as a result of interpretation.

    4. Trace the path through, multiplying the individual compound predicates to achieve a boolean expression such as

    (A+BC) (D+E) (FGH) (IJ) (K) (l) (L).

    5. Multiply out the expression to achieve a sum of products form: ADFGHIJKL+AEFGHIJKL+BCDFGHIJKL+BCEFGHIJKL

    6. Each product term denotes a set of inequalities that if solved will yield an input vector that will drive the routine along the designated path.

    7. Solve any one of the inequality sets for the chosen path and you have found a set of input values for the path.


    8. If you can find a solution, then the path is achievable. 9. If you cant find a solution to any of the sets of inequalities, the path is un achievable. 10. The act of finding a set of solutions to the path predicate expression is called PATH



    1. This is a workable approach, instead of selecting the paths without considering how to sensitize, attempt to choose a covering path set that is easy to sensitize and pick hard to

    sensitize paths only as you must to achieve coverage.

    2. Identify all variables that affect the decision. 3. Classify the predicates as dependent or independent. 4. Start the path selection with un correlated, independent predicates. 5. If coverage has not been achieved using independent uncorrelated predicates, extend the

    path set using correlated predicates.

    6. If coverage has not been achieved extend the cases to those that involve dependent predicates.

    7. Last, use correlated, dependent predicates.


    1. Path instrumentation is what we have to do to confirm that the outcome was achieved by the intended path.

    2. Co-incidental Correctness: The coincidental correctness stands for achieving the desired outcome for wrong reason.

    Figure 2.11: Coincidental Correctness

    The above figure is an example of a routine that, for the (unfortunately) chosen input value (X

    = 16), yields the same outcome (Y = 2) no matter which case we select. Therefore, the tests

    chosen this way will not tell us whether we have achieved coverage. For example, the five

    cases could be totally jumbled and still the outcome would be the same. Path


    Instrumentation is what we have to do to confirm that the outcome was achieved by the

    intended path.

    The types of instrumentation methods include:

    1. Interpretive Trace Program:

    o An interpretive trace program is one that executes every statement in order and records the intermediate values of all calculations, the statement labels traversed etc.

    o If we run the tested routine under a trace, then we have all the information we need to confirm the outcome and, furthermore, to confirm that it was achieved by the intended


    o The trouble with traces is that they give us far more information than we need. In fact, the typical trace program provides so much information that confirming the path from its

    massive output dump is more work than simulating the computer by hand to confirm the


    2. Traversal Marker or Link Marker: o A simple and effective form of instrumentation is called a traversal marker or link marker. o Name every link by a lower case letter. o Instrument the links so that the link's name is recorded when the link is executed. o The succession of letters produced in going from the routine's entry to its exit should, if

    there are no bugs, exactly correspond to the path name.

    Figure 2.12: Single Link Marker Instrumentation

    o Why Single Link Markers aren't enough: Unfortunately, a single link marker may not do the trick because links can be chewed by open bugs.


    Figure 2.13: Why Single Link Markers aren't enough.

    We intended to traverse the ikm path, but because of a rampaging GOTO in the middle of

    the m link, we go to process B. If coincidental correctness is against us, the outcomes will

    be the same and we won't know about the bug.

    Two Link Marker Method: The solution to the problem of single link marker method is to implement two markers per

    link: one at the beginning of each link and on at the end.

    The two link markers now specify the path name and confirm both the beginning and end

    of the link.

    Figure 2.14: Double Link Marker Instrumentation

    Link Counter: A less disruptive (and less informative) instrumentation method is based on counters. Instead of a unique link name to be pushed into a string when the link is

    traversed, we simply increment a link counter. We now confirm that the path length is as

    expected. The same problem that led us to double link markers also leads us to double link






    o A transaction is a unit of work seen from a system user's point of view.

    o A transaction consists of a sequence of operations, some of which are performed

    by a system, persons or devices that are outside of the system.

    o Transaction begins with Birth-that is they are created as a result of some external


    o At the conclusion of the transaction's processing, the transaction is no longer in

    the system.

    o Example of a transaction: A transaction for an online information retrieval

    system might consist of the following steps or tasks:

    Accept input (tentative birth)

    Validate input (birth)

    Transmit acknowledgement to requester

    Do input processing

    Search file

    Request directions from user

    Accept input

    Validate input

    Process request

    Update file

    Transmit output

    Record transaction in log and clean up (death)


    o Transaction flows are introduced as a representation of a system's processing.

    o The methods that were applied to control flow graphs are then used for functional


    o Transaction flows and transaction flow testing are to the independent system

    tester what control flows are path testing are to the programmer.

    o The transaction flow graph is to create a behavioral model of the program that

    leads to functional testing.

    o The transaction flowgraph is a model of the structure of the system's behavior


    o An example of a Transaction Flow is as follows:


    Figure 3.1: An Example of a Transaction Flow

    USAGE: o Transaction flows are indispensable for specifying requirements of complicated

    systems, especially online systems.

    o A big system such as an air traffic control or airline reservation system, has not

    hundreds, but thousands of different transaction flows.

    o The flows are represented by relatively simple flowgraphs, many of which have a

    single straight-through path.

    o Loops are infrequent compared to control flowgraphs.

    o The most common loop is used to request a retry after user input errors. An ATM

    system, for example, allows the user to try, say three times, and will take the card

    away the fourth time.


    o In simple cases, the transactions have a unique identity from the time they're

    created to the time they're completed.

    o In many systems the transactions can give birth to others, and transactions can

    also merge.

    o Births: There are three different possible interpretations of the decision symbol,

    or nodes with two or more out links. It can be a Decision, Biosis or a Mitosis.

    1. Decision: Here the transaction will take one alternative or the other alternative but not both. (See Figure 3.2 (a))

    2. Biosis: Here the incoming transaction gives birth to a new transaction, and both transaction continue on their separate paths, and the parent retains it

    identity. (See Figure 3.2 (b))

    3. Mitosis: Here the parent transaction is destroyed and two new transactions are created.(See Figure 3.2 (c))


    Figure 3.2: Nodes with multiple outlinks

    Mergers: Transaction flow junction points are potentially as troublesome as transaction flow

    splits. There are three types of junctions: (1) Ordinary Junction (2) Absorption (3) Conjugation

    1 Ordinary Junction: An ordinary junction which is similar to the junction in a control flow

    graph. A transaction can arrive either on one link or the other. (See Figure 3.3 (a))

    2 Absorption: In absorption case, the predator transaction absorbs prey transaction. The prey

    gone but the predator retains its identity. (See Figure 3.3 (b))

    3 Conjugation: In conjugation case, the two parent transactions merge to form a new

    daughter. In keeping with the biological flavor this case is called as conjugation.(See Figure

    3.3 (c))

    Figure 3.3: Transaction Flow Junctions and Mergers

    We have no problem with ordinary decisions and junctions. Births, absorptions, and conjugations

    are as problematic for the software designer as they are for the software modeler and the test

    designer; as a consequence, such points have more than their share of bugs. The common

    problems are: lost daughters, wrongful deaths, and illegitimate births.



    o Complicated systems that process a lot of different, complicated transactions

    should have explicit representations of the transactions flows, or the equivalent.

    o Transaction flows are like control flow graphs, and consequently we should

    expect to have them in increasing levels of detail.

    o The system's design documentation should contain an overview section that

    details the main transaction flows.

    o Detailed transaction flows are a mandatory pre requisite to the rational design of a

    system's functional test.


    o Transaction flows are natural agenda for system reviews or inspections.

    o In conducting the walkthroughs, you should:


    Discuss enough transaction types to account for 98%-99% of the

    transaction the system is expected to process.

    Discuss paths through flows in functional rather than technical terms.

    Ask the designers to relate every flow to the specification and to show

    how that transaction, directly or indirectly, follows from the requirements.

    o Make transaction flow testing the corner stone of system functional testing just as

    path testing is the corner stone of unit testing.

    o Select additional flow paths for loops, extreme values, and domain boundaries.

    o Design more test cases to validate all births and deaths.

    o Publish and distribute the selected test paths through the transaction flows as early

    as possible so that they will exert the maximum beneficial effect on the project.


    o Select a set of covering paths (c1+c2) using the analogous criteria you used for

    structural path testing.

    o Select a covering set of paths based on functionally sensible transactions as you

    would for control flow graphs.

    o Try to find the most tortuous, longest, strangest path from the entry to the exit of

    the transaction flow.


    o Most of the normal paths are very easy to sensitize-80% - 95% transaction flow

    coverage (c1+c2) is usually easy to achieve.

    o The remaining small percentage is often very difficult.

    o Sensitization is the act of defining the transaction. If there are sensitization

    problems on the easy paths, then bet on either a bug in transaction flows or a

    design bug.


    o Instrumentation plays a bigger role in transaction flow testing than in unit path


    o The information of the path taken for a given transaction must be kept with that

    transaction and can be recorded by a central transaction dispatcher or by the

    individual processing modules.

    o In some systems, such traces are provided by the operating systems or a running



    DATA FLOW TESTING: o Data flow testing is the name given to a family of test strategies based on

    selecting paths through the program's control flow in order to explore sequences

    of events related to the status of data objects.

    o For example, pick enough paths to assure that every data object has been

    initialized prior to use or that all defined objects have been used for something.

    o Motivation: It is our belief that, just as one would not feel confident about a

    program without executing every statement in it as part of some test, one should


    not feel confident about a program without having seen the effect of using the

    value produced by each and every computation.

    DATA FLOW MACHINES: o There are two types of data flow machines with different architectures. (1) Von

    Neumann machines (2) Multi-instruction, multi-data machines (MIMD).

    o Von Neumann Machine Architecture: Most computers today are von-neumann machines.

    This architecture features interchangeable storage of instructions and data

    in the same memory units.

    The Von Neumann machine Architecture executes one instruction at a

    time in the following, micro instruction sequence:

    Fetch instruction from memory

    Interpret instruction

    Fetch operands

    Process or Execute

    Store result

    Increment program counter

    GOTO 1

    o Multi-instruction, Multi-data machines (MIMD) Architecture:

    These machines can fetch several instructions and objects in parallel.

    They can also do arithmetic and logical operations simultaneously on

    different data objects.

    The decision of how to sequence them depends on the compiler.

    BUG ASSUMPTION: The bug assumption for data-flow testing strategies is that control flow is generally

    correct and that something has gone wrong with the software so that data objects are not

    available when they should be, or silly things are being done to data objects.

    o Also, if there is a control-flow problem, we expect it to have symptoms that can

    be detected by data-flow analysis.

    o Although we'll be doing data-flow testing, we won't be using data flow graphs as

    such. Rather, we'll use an ordinary control flow graph annotated to show what

    happens to the data objects of interest at the moment.


    o The data flow graph is a graph consisting of nodes and directed links.

    o We will use a control graph to show what happens to data objects of interest at

    that moment.

    o Our objective is to expose deviations between the data flows we have and the data

    flows we want.


    Figure 3.4: Example of a data flow graph

    o Data Object State and Usage: Data Objects can be created, killed and used.

    They can be used in two distinct ways: (1) In a Calculation (2) As a part of

    a Control Flow Predicate.

    The following symbols denote these possibilities:

    1. Defined: d - defined, created, initialized etc 2. Killed or undefined: k - killed, undefined, released etc 3. Usage: u - used for something (c - used in Calculations, p - used in

    a predicate)

    1. Defined (d): An object is defined explicitly when it appears in a data


    Or implicitly when it appears on the left hand side of the


    It is also to be used to mean that a file has been opened.

    A dynamically allocated object has been allocated.

    Something is pushed on to the stack.

    A record written.

    2. Killed or Undefined (k): An object is killed on undefined when it is released or otherwise

    made unavailable.


    When its contents are no longer known with certitude (with

    absolute certainty / perfectness).

    Release of dynamically allocated objects back to the availability


    Return of records.

    The old top of the stack after it is popped.

    An assignment statement can kill and redefine immediately. For

    example, if A had been previously defined and we do a new

    assignment such as A : = 17, we have killed A's previous value and

    redefined A

    3. Usage (u): A variable is used for computation (c) when it appears on the right

    hand side of an assignment statement.

    A file record is read or written.

    It is used in a Predicate (p) when it appears directly in a predicate.


    An anomaly is denoted by a two-character sequence of actions. For example, ku means that the

    object is killed and then used, where as dd means that the object is defined twice without an

    intervening usage.

    What is an anomaly is depend on the application.

    There are nine possible two-letter combinations for d, k and u. some are bugs, some are

    suspicious, and some are okay.

    1 dd :- probably harmless but suspicious. Why define the object twice without an intervening


    2 dk :- probably a bug. Why define the object without using it?

    3 du :- the normal case. The object is defined and then used.

    4 kd :- normal situation. An object is killed and then redefined.

    5 kk :- harmless but probably buggy. Did you want to be sure it was really killed?

    6 ku :- a bug. the object doesnot exist.

    7 ud :- usually not a bug because the language permits reassignment at almost any time.

    8 uk :- normal situation.

    9 uu :- normal situation.

    In addition to the two letter situations, there are six single letter situations.We will use a leading

    dash to mean that nothing of interest (d,k,u) occurs prior to the action noted along the entry-exit

    path of interest.

    A trailing dash to mean that nothing happens after the point of interest to the exit.

    They possible anomalies are: 1 -k :- possibly anomalous because from the entrance to this point on the path, the

    variable had not been defined. We are killing a variable that does not exist.

    2 -d :- okay. This is just the first definition along this path.

    3 -u :- possibly anomalous. Not anomalous if the variable is global and has been

    previously defined.


    4 k- :- not anomalous. The last thing done on this path was to kill the variable.

    5 d- :- possibly anomalous. The variable was defined and not used on this path. But

    this could be a global definition.

    6 u- :- not anomalous. The variable was used but not killed on this path. Although this

    sequence is not anomalous, it signals a frequent kind of bug. If d and k mean

    dynamic storage allocation and return respectively, this could be an instance in

    which a dynamically allocated object was not returned to the pool after use.


    Data flow anomaly model prescribes that an object can be in one of four distinct states:

    0. K :- undefined, previously killed, doesnot exist 1. D :- defined but not yet used for anything 2. U :- has been used for computation or in predicate 3. A :- anomalous

    These capital letters (K, D, U, A) denote the state of the variable and should not be confused

    with the program action, denoted by lower case letters.

    Unforgiving Data - Flow Anomaly Flow Graph: Unforgiving model, in which once a variable

    becomes anomalous it can never return to a state of grace.

    Figure 3.5: Unforgiving Data Flow Anomaly State Graph Assume that the variable starts in the K state - that is, it has not been defined or does not exist. If

    an attempt is made to use it or to kill it (e.g., say that we're talking about opening, closing, and

    using files and that 'killing' means closing), the object's state becomes anomalous (state A) and,

    once it is anomalous, no action can return the variable to a working state.

    If it is defined (d), it goes into the D, or defined but not yet used, state. If it has been defined (D)

    and redefined (d) or killed without use (k), it becomes anomalous, while usage (u) brings it to the

    U state. If in U, redefinition (d) brings it to D, u keeps it in U, and k kills it.

    Forgiving Data - Flow Anomaly Flow Graph: Forgiving model is an alternate model where

    redemption (recover) from the anomalous state is possible


    Figure 3.6: Forgiving Data Flow Anomaly State Graph

    This graph has three normal and three anomalous states and he considers the kk sequence not to

    be anomalous. The difference between this state graph and Figure 3.5 is that redemption is

    possible. A proper action from any of the three anomalous states returns the variable to a useful

    working state.

    The point of showing you this alternative anomaly state graph is to demonstrate that the specifics

    of an anomaly depends on such things as language, application, context, or even your frame of

    mind. In principle, you must create a new definition of data flow anomaly (e.g., a new state

    graph) in each situation. You must at least verify that the anomaly definition behind the theory or

    imbedded in a data flow anomaly test tool is appropriate to your situation.


    Static analysis is analysis done on source code without actually executing it. For example: source

    code syntax error detection is the static analysis result.

    Dynamic analysis is done on the fly as the program is being executed and is based on

    intermediate values that result from the program's execution. For example: a division by zero

    warning is the dynamic result.

    If a problem, such as a data flow anomaly, can be detected by static analysis methods, then it

    doesnt belongs in testing - it belongs in the language processor.

    There is actually a lot more static analysis for data flow analysis for data flow anomalies going

    on in current language processors.

    For example, language processors which force variable declarations can detect (-u) and (ku)

    anomalies.But still there are many things for which current notions of static analysis are


    Why Static Analysis isn't enough? There are many things for which current notions of static

    analysis are inadequate. They are:


    Dead Variables: Although it is often possible to prove that a variable is dead or alive at a

    given point in the program, the general problem is unsolvable.

    Arrays: Arrays are problematic in that the array is defined or killed as a single object, but

    reference is to specific locations within the array. Array pointers are usually dynamically

    calculated, so there's no way to do a static analysis to validate the pointer value. In many

    languages, dynamically allocated arrays contain garbage unless explicitly initialized and

    therefore, -u anomalies are possible.

    Records and Pointers: The array problem and the difficulty with pointers is a special case

    of multipart data structures. We have the same problem with records and the pointers to

    them. Also, in many applications we create files and their names dynamically and there's no

    way to determine, without execution, whether such objects are in the proper state on a given

    path or, for that matter, whether they exist at all.

    Dynamic Subroutine and Function Names in a Call: subroutine or function name is a

    dynamic variable in a call. What is passed, or a combination of subroutine names and data

    objects, is constructed on a specific path. There's no way, without executing the path, to

    determine whether the call is correct or not.

    False Anomalies: Anomalies are specific to paths. Even a "clear bug" such as ku may not be

    a bug if the path along which the anomaly exist is unachievable. Such "anomalies" are false

    anomalies. Unfortunately, the problem of determining whether a path is or is not achievable

    is unsolvable.

    Recoverable Anomalies and Alternate State Graphs: What constitutes an anomaly

    depends on context, application, and semantics. How does the compiler know which model I

    have in mind? It can't because the definition of "anomaly" is not fundamental. The language

    processor must have a built-in anomaly definition with which you may or may not (with

    good reason) agree.

    Concurrency, Interrupts, System Issues: As soon as we get away from the simple single-

    task uniprocessor environment and start thinking in terms of systems, most anomaly issues

    become vastly more complicated.

    How often do we define or create data objects at an interrupt level so that they can be

    processed by a lower-priority routine? Interrupts can make the "correct" anomalous and the

    "anomalous" correct. True concurrency (as in an MIMD machine) and pseudo concurrency

    (as in multiprocessing) systems can do the same to us. Much of integration and system

    testing is aimed at detecting data-flow anomalies that cannot be detected in the context of a

    single routine.

    Although static analysis methods have limits, they are worth using and a continuing trend in

    language processor design has been better static analysis methods, especially for data flow

    anomaly detection. That's good because it means there's less for us to do as testers and we

    have far too much to do as it is.



    The data flow model is based on the program's control flow graph - Don't confuse that with the

    program's data flow graph.

    Here we annotate each link with symbols (for example, d, k, u, c, and p) or sequences of symbols

    (for example, dd, du, ddd) that denote the sequence of data operations on that link with respect to

    the variable of interest. Such annotations are called link weights.

    The control flow graph structure is same for every variable: it is the weights that change.

    Components of the model:

    1. To every statement there is a node, whose name is unique. Every node has at least one outlink and at least one inlink except for exit nodes and entry nodes.

    2. Exit nodes are dummy nodes placed at the outgoing arrowheads of exit statements (e.g., END, RETURN), to complete the graph. Similarly, entry nodes are dummy nodes placed

    at entry statements (e.g., BEGIN) for the same reason.

    3. The outlink of simple statements (statements with only one outlink) are weighted by the proper sequence of data-flow actions for that statement. Note that the sequence can

    consist of more than one letter. For example, the assignment statement A:= A + B in most

    languages is weighted by cd or possibly ckd for variable A. Languages that permit

    multiple simultaneous assignments and/or compound statements can have anomalies

    within the statement. The sequence must correspond to the order in which the object code

    will be executed for that variable.

    4. Predicate nodes (e.g., IF-THEN-ELSE, DO WHILE, CASE) are weighted with the p - use(s) on every outlink, appropriate to that outlink.

    5. Every sequence of simple statements (e.g., a sequence of nodes with one inlink and one outlink) can be replaced by a pair of nodes that has, as weights on the link between them,

    the concatenation of link weights.

    6. If there are several data-flow actions on a given link for a given variable, then the weight of the link is denoted by the sequence of actions on that link for that variable.

    7. Conversely, a link with several data-flow actions on it can be replaced by a succession of equivalent links, each of which has at most one data-flow action for any variable.

    Let us consider the example:

    Figure 3.7: Program Example (PDL)


    Figure 3.8: Unannotated flow graph for example program in Figure 3.7

    Figure 3.9: Control flow graph annotated for X and Y data flows.

    Figure 3.10: Control flow graph annotated for Z data flow.

    Figure 3.11: Control flow graph annotated for V data flow.




    o Data Flow Testing Strategies are structural strategies.

    o In contrast to the path-testing strategies, data-flow strategies take into account

    what happens to data objects on the links in addition to the raw connectivity of the


    o In other words, data flow strategies require data-flow link weights (d,k,u,c,p).

    o Data Flow Testing Strategies are based on selecting test path segments (also

    called sub paths) that satisfy some characteristic of data flows for all data objects.

    o For example, all sub paths that contain a d (or u, k, du, dk).

    o A strategy X is stronger than another strategy Y if all test cases produced under

    Y are included in those produced under X - conversely for weaker.

    TERMINOLOGY: 1. Definition-Clear Path Segment, with respect to variable X, is a connected

    sequence of links such that X is (possibly) defined on the first link and not

    redefined or killed on any subsequent link of that path segment. ll paths in Figure

    3.9 are definition clear because variables X and Y are defined only on the first

    link (1,3) and not thereafter. In Figure 3.10, we have a more complicated

    situation. The following path segments are definition-clear: (1,3,4), (1,3,5),

    (5,6,7,4), (7,8,9,6,7), (7,8,9,10), (7,8,10), (7,8,10,11). Subpath (1,3,4,5) is not

    definition-clear because the variable is defined on (1,3) and again on (4,5). For

    practice, try finding all the definition-clear subpaths for this routine (i.e., for all


    2. Loop-Free Path Segment is a path segment for which every node in it is visited atmost once. For Example, path (4,5,6,7,8,10) in Figure 3.10 is loop free, but path

    (10,11,4,5,6,7,8,10,11,12) is not because nodes 10 and 11 are each visited twice.

    3. Simple path segment is a path segment in which at most one node is visited twice. For example, in Figure 3.10, (7,4,5,6,7) is a simple path segment. A simple

    path segment is either loop-free or if there is a loop, only one node is involved.

    4. A du path from node i to k is a path segment such that if the last link has a computational use of X, then the path is simple and definition-clear; if the

    penultimate (last but one) node is j - that is, the path is (i,p,q,...,r,s,t,j,k) and link

    (j,k) has a predicate use - then the path from i to j is both loop-free and definition-


    STRATEGIES: The structural test strategies discussed below are based on the program's

    control flow graph. They differ in the extent to which predicate uses and/or computational uses

    of variables are included in the test set. Various types of data flow testing strategies in decreasing

    order of their effectiveness are:

    All - du Paths (ADUP): The all-du-paths (ADUP) strategy is the strongest data-flow testing

    strategy discussed here. It requires that every du path from every definition of every variable to

    every some test.


    For variable X and Y:In Figure 3.9, because variables X and Y are used only on link (1,3), any test

    that starts at the entry satisfies this criterion (for variables X and Y, but not for all variables as

    required by the strategy).

    For variable Z: The situation for variable Z (Figure 3.10) is more complicated because the

    variable is redefined in many places. For the definition on link (1,3) we must exercise paths that

    include subpaths (1,3,4) and (1,3,5). The definition on link (4,5) is covered by any path that

    includes (5,6), such as subpath (1,3,4,5,6, ...). The (5,6) definition requires paths that include

    subpaths (5,6,7,4) and (5,6,7,8).

    For variable V: Variable V (Figure 3.11) is defined only once on link (1,3). Because V has a

    predicate use at node 12 and the subsequent path to the end must be forced for both directions at

    node 12, the all-du-paths strategy for this variable requires that we exercise all loop-free

    entry/exit paths and at least one path that includes the loop caused by (11,4).

    Note that we must test paths that include both subpaths (3,4,5) and (3,5) even though neither of

    these has V definitions. They must be included because they provide alternate du paths to the V

    use on link (5,6). Although (7,4) is not used in the test set for variable V, it will be included in

    the test set that covers the predicate uses of array variable V() and U.

    The all-du-paths strategy is a strong criterion, but it does not take as many tests as it might seem

    at first because any one test simultaneously satisfies the criterion for several definitions and uses

    of several different variables.

    All Uses Startegy (AU):The all uses strategy is that at least one definition clear path from every

    definition of every variable to every use of that definition be exercised under some test.

    Just as we reduced our ambitions by stepping down from all paths (P) to branch coverage (C2),

    say, we can reduce the number of test cases by asking that the test set should include at least one

    path segment from every definition to every use that can be reached by that definition.

    For variable V: In Figure 3.11, ADUP requires that we include subpaths (3,4,5) and (3,5) in

    some test because subsequent uses of V, such as on link (5,6), can be reached by either

    alternative. In AU either (3,4,5) or (3,5) can be used to start paths, but we don't have to use both.

    Similarly, we can skip the (8,10) link if we've included the (8,9,10) subpath.

    Note the hole. We must include (8,9,10) in some test cases because that's the only way to reach

    the c use at link (9,10) - but suppose our bug for variable V is on link (8,10) after all? Find a

    covering set of paths under AU for Figure 3.11.

    All p-uses/some c-uses strategy (APU+C) : For every variable and every definition of that

    variable, include at least one definition free path from the definition to every predicate use; if

    there are definitions of the variables that are not covered by the above prescription, then add

    computational use test cases as required to cover every definition.


    For variable Z:In Figure 3.10, for APU+C we can select paths that all take the upper link (12,13)

    and therefore we do not cover the c-use of Z: but that's okay according to the strategy's definition

    because every definition is covered.

    Links (1,3), (4,5), (5,6), and (7,8) must be included because they contain definitions for variable

    Z. Links (3,4), (3,5), (8,9), (8,10), (9,6), and (9,10) must be included because they contain

    predicate uses of Z. Find a covering set of test cases under APU+C for all variables in this

    example - it only takes two tests.

    For variable V:In Figure 3.11, APU+C is achieved for V by

    (1,3,5,6,7,8,10,11,4,5,6,7,8,10,11,12[upper], 13,2) and (1,3,5,6,7,8,10,11,12[lower], 13,2). Note

    that the c-use at (9,10) need not be included under the APU+C criterion.

    All c-uses/some p-uses strategy (ACU+P) : The all c-uses/some p-uses strategy (ACU+P) is to

    first ensure coverage by computational use cases and if any definition is not covered by the

    previously selected paths, add such predicate use cases as are needed to assure that every

    definition is included in some test.

    For variable Z: In Figure 3.10, ACU+P coverage is achieved for Z by path (1,3,4,5,6,7,8,10,

    11,12,13[lower], 2), but the predicate uses of several definitions are not covered. Specifically,

    the (1,3) definition is not covered for the (3,5) p-use, the (7,8) definition is not covered for the

    (8,9), (9,6) and (9, 10) p-uses.

    The above examples imply that APU+C is stronger than branch coverage but ACU+P may be

    weaker than, or incomparable to, branch coverage.

    All Definitions Strategy (AD) : The all definitions strategy asks only every definition of every

    variable be covered by atleast one use of that variable, be that use a computational use or a

    predicate use.

    For variable Z: Path (1,3,4,5,6,7,8, . . .) satisfies this criterion for variable Z, whereas any entry/exit path satisfies it for variable V.

    From the definition of this strategy we would expect it to be weaker than both ACU+P and


    1. All Predicate Uses (APU), All Computational Uses (ACU) Strategies : The all predicate uses strategy is derived from APU+C strategy by dropping the requirement that we include a c-

    use for the variable if there are no p-uses for the variable. The all computational uses strategy is

    derived from ACU+P strategy by dropping the requirement that we include a p-use for the

    variable if there are no c-uses for the variable.

    It is intuitively obvious that ACU should be weaker than ACU+P and that APU should be

    weaker than APU+C.



    Figure 3.12compares path-flow and data-flow testing strategies. The arrows denote that the

    strategy at the arrow's tail is stronger than the strategy at the arrow's head

    Figure 3.12: Relative Strength of Structural Test Strategies.

    o The right-hand side of this graph, along the path from "all paths" to "all

    statements" is the more interesting hierarchy for practical applications.

    o Note that although ACU+P is stronger than ACU, both are incomparable to the

    predicate-biased strategies. Note also that "all definitions" is not comparable to

    ACU or APU.


    o A (static) program slice is a part of a program (e.g., a selected set of statements)

    defined with respect to a given variable X (where X is a simple variable or a data

    vector) and a statement i: it is the set of all statements that could (potentially,

    under static analysis) affect the value of X at statement i - where the influence of a

    faulty statement could result from an improper computational use or predicate use

    of some other variables at prior statements.

    o If X is incorrect at statement i, it follows that the bug must be in the program slice

    for X with respect to i

    o A program dice is a part of a slice in which all statements which are known to be

    correct have been removed.

    o In other words, a dice is obtained from a slice by incorporating information

    obtained through testing or experiment (e.g., debugging).


    o The debugger first limits her scope to those prior statements that could have

    caused the faulty value at statement i (the slice) and then eliminates from further

    consideration those statements that testing has shown to be correct.

    o Debugging can be modeled as an iterative procedure in which slices are further

    refined by dicing, where the dicing information is obtained from ad hoc tests

    aimed primarily at eliminating possibilities. Debugging ends when the dice has

    been reduced to the one faulty statement.

    o Dynamic slicing is a refinement of static slicing in which only statements on

    achievable paths to the statement in question are included.






    o Domain: In mathematics, domain is a set of possible values of an independent

    variable or the variables of a function.

    o Programs as input data classifiers: domain testing attempts to determine whether

    the classification is or is not correct.

    o Domain testing can be based on specifications or equivalent implementation


    o If domain testing is based on specifications, it is a functional test technique.

    o If domain testing is based implementation details, it is a structural test technique.

    o For example, you're doing domain testing when you check extreme values of an

    input variable.

    All inputs to a program can be considered as if they are numbers. For example, a

    character string can be treated as a number by concatenating bits and looking at them as if

    they were a binary integer. This is the view in domain testing, which is why this strategy

    has a mathematical flavor.

    THE MODEL: The following figure is a schematic representation of domain testing.

    Figure 4.1: Schematic Representation of Domain Testing.

    o Before doing whatever it does, a routine must classify the input and set it moving

    on the right path.

    o An invalid input (e.g., value too big) is just a special processing case called


    o The input then passes to a hypothetical subroutine rather than on calculations.

    o In domain testing, we focus on the classification aspect of the routine rather than

    on the calculations.

    o Structural knowledge is not needed for this model - only a consistent, complete

    specification of input values for each case.

    o We can infer that for each case there must be at least one path to process that case.



    o An input domain is a set.

    o If the source language supports set definitions (E.g. PASCAL set types and C

    enumerated types) less testing is needed because the compiler does much of it for


    o Domain testing does not work well with arbitrary discrete sets of data objects.

    o Domain for a loop-free program corresponds to a set of numbers defined over the

    input vector.


    o In domain testing, predicates are assumed to be interpreted in terms of input

    vector variables.

    o If domain testing is applied to structure, then predicate interpretation must be

    based on actual paths through the routine - that is, based on the implementation

    control flow graph.

    o Conversely, if domain testing is applied to specifications, interpretation is based

    on a specified data flow graph for the routine; but usually, as is the nature of

    specifications, no interpretation is needed because the domains are specified


    o For every domain, there is at least one path through the routine.

    o There may be more than one path if the domain consists of disconnected parts or

    if the domain is defined by the union of two or more domains.

    o Domains are defined their boundaries. Domain boundaries are also where most

    domain bugs occur.

    o For every boundary there is at least one predicate that specifies what numbers

    belong to the domain and what numbers don't.

    For example, in the statement IF x>0 THEN ALPHA ELSE BETA we know that

    numbers greater than zero belong to ALPHA processing domain(s) while zero and

    smaller numbers belong to BETA domain(s).

    o A domain may have one or more boundaries - no matter how many variables

    define it. For example, if the predicate is x2 + y2 < 16, the domain is the inside of

    a circle of radius 4 about the origin. Similarly, we could define a spherical domain

    with one boundary but in three variables.

    o Domains are usually defined by many boundary segments and therefore by many

    predicates. i.e. the set of interpreted predicates traversed on that path (i.e., the

    path's predicate expression) defines the domain's boundaries.


    o A domain boundary is closed with respect to a domain if the points on the

    boundary belong to the domain.

    o If the boundary points belong to some other domain, the boundary is said to be


    o Figure 4.2 shows three situations for a one-dimensional domain - i.e., a domain

    defined over one input variable; call it x

    The importance of domain closure is that incorrect closure bugs are frequent domain bugs. For

    example, x >= 0 when x > 0 was intended


    Figure 4.2: Open and Closed Domains.

    DOMAIN DIMENSIONALITY: o Every input variable adds one dimension to the domain.

    o One variable defines domains on a number line.

    o Two variables define planar domains.

    o Three variables define solid domains.

    o Every new predicate slices through previously defined domains and cuts them in


    o Every boundary slices through the input vector space with a dimensionality which

    is less than the dimensionality of the space.

    o Thus, planes are cut by lines and points, volumes by planes, lines and points and

    n-spaces by hyperplanes.

    BUG ASSUMPTION: o The bug assumption for the domain testing is that processing is okay but the

    domain definition is wrong.

    o An incorrectly implemented domain means that boundaries are wrong, which may

    in turn mean that control flow predicates are wrong.

    o Many different bugs can result in domain errors. Some of them are:

    Domain Errors:

    Double Zero Representation: In computers or Languages that have a

    distinct positive and negative zero, boundary errors for negative zero are


    Floating point zero check: A floating point number can equal zero only if

    the previous definition of that number set it to zero or if it is subtracted

    from itself or multiplied by zero. So the floating point zero check to be

    done against an epsilon value.

    Contradictory domains: An implemented domain can never be

    ambiguous or contradictory, but a specified domain can. A contradictory


    domain specification means that at least two supposedly distinct domains


    Ambiguous domains: Ambiguous domains means that union of the

    domains is incomplete. That is there are missing domains or holes in the

    specified domains. Not specifying what happens to points on the domain

    boundary is a common ambiguity.

    Over specified Domains: his domain can be overloaded with so many

    conditions that the result is a null domain. Another way to put it is to say

    that the domain's path is unachievable.

    Boundary Errors: Errors caused in and around the boundary of a domain.

    Example, boundary closure bug, shifted, tilted, missing, extra boundary.

    Closure Reversal: A common bug. The predicate is defined in terms of

    >=. The programmer chooses to implement the logical complement and

    incorrectly uses = 0 is incorrectly

    negated as x


    an example of a compound predicate that specifies one boundary, consider: x = 0 AND y

    >= 7 AND y 14. Treat

    compound predicates with respect because theyre more complicated than they seem.

    o Functional Homogeneity of Bugs: Whatever the bug is, it will not change the

    functional form of the boundary predicate. For example, if the predicate is ax >=

    b, the bug will be in the value of a or b but it will not change the predicate to ax

    >= b, say.

    o Linear Vector Space: Most papers on domain testing, assume linear boundaries -

    not a bad assumption because in practice most boundary predicates are linear.

    o Loop Free Software: Loops are problematic for domain testing. The trouble with

    loops is that each iteration can result in a different predicate expression (after

    interpretation), which means a possible domain boundary change.



    o Where do these domains come from? Domains are and will be defined by an imperfect iterative process aimed at

    achieving (user, buyer, voter) satisfaction.

    o Implemented domains can't be incomplete or inconsistent. Every input will be

    processed (rejection is a process), possibly forever. Inconsistent domains will be

    made consistent.

    o Conversely, specified domains can be incomplete and/or inconsistent. Incomplete

    in this context means that there are input vectors for which no path is specified,

    and inconsistent means that there are at least two contradictory specifications over

    the same segment of the input space.

    o Some important properties of nice domains are: Linear, Complete, Systematic,

    And Orthogonal, Consistently closed, Convex and simply connected. o To the extent that domains have these properties domain testing is easy as testing


    o The bug frequency is lesser for nice domain than for ugly domains.

    Figure 4.3: Nice Two-Dimensional Domains.



    o Nice domain boundaries are defined by linear inequalities or equations.

    o The impact on testing stems from the fact that it takes only two points to

    determine a straight line and three points to determine a plane and in general n+ 1

    point to determine an n-dimensional hyper plane.

    o In practice more than 99.99% of all boundary predicates are either linear or can be

    linearized by simple variable transformations.


    o Nice domain boundaries are complete in that they span the number space from

    plus to minus infinity in all dimensions.

    o Figure 4.4 shows some incomplete boundaries. Boundaries A and E have gaps.

    o Such boundaries can come about because the path that hypothetically corresponds

    to them is unachievable, because inputs are constrained in such a way that such

    values can't exist, because of compound predicates that define a single boundary,

    or because redundant predicates convert such boundary values into a null set.

    o The advantage of complete boundaries is that one set of tests is needed to confirm

    the boundary no matter how many domains it bounds.

    o If the boundary is chopped up and has holes in it, then every segment of that

    boundary must be tested for every domain it bounds.

    Figure 4.4: Incomplete Domain Boundaries.


    o Systematic boundary means that boundary inequalities related by a simple

    function such as a constant.

    In Figure 4.3 for example, the domain boundaries for u and v differ only by a



    o where fi is an arbitrary linear function, X is the input vector, ki and c are constants,

    and g(i,c) is a decent function over i and c that yields a constant, such as k + ic.

    o The first example is a set of parallel lines, and the second example is a set of

    systematically (e.g., equally) spaced parallel lines (such as the spokes of a wheel,

    if equally spaced in angles, systematic).

    o If the boundaries are systematic and if you have one tied down and generate tests

    for it, the tests for the rest of the boundaries in that set can be automatically



    o Two boundary sets U and V (See Figure 4.3) are said to be orthogonal if every

    inequality in V is perpendicular to every inequality in U.

    o If two boundary sets are orthogonal, then they can be tested independently

    o In Figure 4.3 we have six boundaries in U and four in V. We can confirm the

    boundary properties in a number of tests proportional to 6 + 4 = 10 (O(n)). If we

    tilt the boundaries to get Figure 4.5,

    o we must now test the intersections. We've gone from a linear number of cases to a

    quadratic: from O(n) to O(n2).

    Figure 4.5: Tilted Boundaries.

    Figure 4.6: Linear, Non-orthogonal Domain Boundaries.


    o Actually, there are two different but related orthogonality conditions. Sets of

    boundaries can be orthogonal to one another but not orthogonal to the coordinate

    axes (condition 1), or boundaries can be orthogonal to the coordinate axes

    (condition 2).


    o Figure 4.6 shows another desirable domain property: boundary closures are

    consistent and systematic.

    o The shaded areas on the boundary denote that the boundary belongs to the domain

    in which the shading lies - e.g., the boundary lines belong to the domains on the


    o Consistent closure means that there is a simple pattern to the closures - for

    example, using the same relational operator for all boundaries of a set of parallel



    o A geometric figure (in any number of dimensions) is convex if you can take two

    arbitrary points on any two different boundaries, join them by a line and all points

    on that line lie within the figure.

    o Nice domains are convex; dirty domains aren't.

    o You can smell a suspected concavity when you see phrases such as: ". . . except if

    . . .," "However . . .," ". . . but not. . . ." In programming, it's often the buts in the

    specification that kill you.

    SIMPLY CONNECTED: o Nice domains are simply connected; that is, they are in one piece rather than

    pieces all over the place interspersed with other domains.

    o Simple connectivity is a weaker requirement than convexity; if a domain is

    convex it is simply connected, but not vice versa.

    o Consider domain boundaries defined by a compound predicate of the (Boolean)

    form ABC. Say that the input space is divided into two domains, one defined by

    ABC and, therefore, the other defined by its negation.

    o For example, suppose we define valid numbers as those lying between 10 and 17

    inclusive. The invalid numbers are the disconnected domain consisting of

    numbers less than 10 and greater than 17.

    o Simple connectivity, especially for default cases, may be impossible.


    o Some domains are born ugly and some are uglified by bad specifications.

    o Every simplification of ugly domains by programmers can be either good or bad.

    o Programmers in search of nice solutions will "simplify" essential complexity out

    of existence. Testers in search of brilliant insights will be blind to essential

    complexity and therefore miss important cases.

    o If the ugliness results from bad specifications and the programmer's simplification

    is harmless, then the programmer has made ugly good.


    o But if the domain's complexity is essential (e.g., the income tax code), such

    "simplifications" constitute bugs.

    o Nonlinear boundaries are so rare in ordinary programming that there's no

    information on how programmers might "correct" such boundaries if they're


    AMBIGUITIES AND CONTRADICTIONS: o Domain ambiguities are holes in the input space.

    o The holes may lie within the domains or in cracks between domains.

    o Two kinds of contradictions are possible: overlapped domain specifications and

    overlapped closure specifications

    o Figure 4.7c shows overlapped domains and Figure 4.7d shows dual closure


    Figure 4.7: Domain Ambiguities and Contradictions.


    o The programmer's and tester's reaction to complex domains is the same - simplify

    o There are three generic cases: concavities, holes and disconnected pieces.

    o Programmers introduce bugs and testers misdesign test cases by: smoothing out

    concavities (Figure 4.8a), filling in holes (Figure 4.8b), and joining disconnected

    pieces (Figure 4.8c).

    Figure 4.8: Simplifying the topology.



    o If domain boundaries are parallel but have closures that go every which way (left,

    right, left . . .) the natural reaction is to make closures go the same way (see

    Figure 4.9).

    Figure 4.9: Forcing Closure Consistency.


    DOMAIN TESTING STRATEGY: The domain-testing strategy is simple, although

    possibly tedious (slow).

    o Domains are defined by their boundaries; therefore, domain testing concentrates

    test points on or near boundaries.

    o Classify what can go wrong with boundaries, then define a test strategy for each

    case. Pick enough points to test for all recognized kinds of boundary errors.

    o Because every boundary serves at least two different domains, test points used to

    check one domain can also be used to check adjacent domains. Remove redundant

    test points.

    o Run the tests and by posttest analysis (the tedious part) determine if any

    boundaries are faulty and if so, how.

    o Run enough tests to verify every boundary of every domain.


    o An interior point (Figure 4.10) is a point in the domain such that all points within

    an arbitrarily small distance (called an epsilon neighborhood) are also in the


    o A boundary point is one such that within an epsilon neighborhood there are

    points both in the domain and not in the domain.

    o An extreme point is a point that does not lie between any two other arbitrary but

    distinct points of a (convex) domain.


    Figure 4.10: Interior, Boundary and Extreme points.

    o An on point is a point on the boundary.

    o If the domain boundary is closed, an off point is a point near the boundary but in

    the adjacent domain.

    o If the boundary is open, an off point is a point near the boundary but in the

    domain being tested; see Figure 4.11. You can remember this by the acronym

    COOOOI: Closed Off Outside, Open Off Inside.

    Figure 4.11: On points and Off points.

    o Figure 4.12 shows generic domain bugs: closure bug, shifted boundaries, tilted

    boundaries, extra boundary, missing boundary.


    Figure 4.12: Generic Domain Bugs.


    The closure can be wrong (i.e., assigned to the wrong domain) or the boundary (a point in this

    case) can be shifted one way or the other, we can be missing a boundary, or we can have an extra


    1. Figure 4.13 shows possible domain bugs for a one-dimensional open domain boundary.

    2. In Figure 4.13a we assumed that the boundary was to be open for A. The bug we're looking for is a closure error, which converts > to >= or < to


    Figure 4.13: One Dimensional Domain Bugs, Open Boundaries.

    4. Figure 4.13d shows a shift the other way. The on point doesn't tell us anything because the boundary shift doesn't change the fact that the test point will be

    processed in B. To detect this shift we need a point close to the boundary but

    within A. The boundary is open, therefore by definition, the off point is in A

    (Open Off Inside).

    5. The same open off point also suffices to detect a missing boundary because what should have been processed in A is now processed in B.

    6. To detect an extra boundary we have to look at two domain boundaries. In this context an extra boundary means that A has been split in two. The two off points

    that we selected before (one for each boundary) does the job. If point C had been

    a closed boundary, the on test point at C would do it.

    7. For closed domains look at Figure 4.14. As for the open boundary, a test point on the boundary detects the closure bug. The rest of the cases are similar to the open

    boundary, except now the strategy requires off points just outside the domain.


    Figure 4.14: One Dimensional Domain Bugs, Closed Boundaries.


    1. Figure 4.15 shows possible domain boundary bugs for a two-dimensional domain. 2. A and B are adjacent domains and the boundary is closed with respect to A, which

    means that it is open with respect to B.

    Figure 4.15: Two Dimensional Domain Bugs.

    3. For Closed Boundaries: Closure Bug: Figure 4.15a shows a faulty closure, such as might be caused by

    using a wrong operator (for example, x >= k when x > k was intended, or vice


    versa). The two on points detect this bug because those values will get B rather

    than A processing.

    1. Shifted Boundary: In Figure 4.15b the bug is a shift up, which converts part of domain B into A processing, denoted by A'. This result is caused

    by an incorrect constant in a predicate, such as x + y >= 17 when x + y >=

    7 was intended. The off point (closed off outside) catches this bug. Figure

    4.15c shows a shift down that is caught by the two on points.

    2. Tilted Boundary: A tilted boundary occurs when coefficients in the boundary inequality are wrong. For example, 3x + 7y > 17 when 7x + 3y >

    17 was intended. Figure 4.15d has a tilted boundary, which creates

    erroneous domain segments A' and B'. In this example the bug is caught

    by the left on point.

    3. Extra Boundary: An extra boundary is created by an extra predicate. An extra boundary will slice through many different domains and will

    therefore cause many test failures for the same bug. The extra boundary in

    Figure 4.15e is caught by two on points, and depending on which way the

    extra boundary goes, possibly by the off point also.

    4. Missing Boundary: A missing boundary is created by leaving a boundary predicate out. A missing boundary will merge different domains and will

    cause many test failures although there is only one bug. A missing

    boundary, shown in Figure 4.15f, is caught by the two on points because

    the processing for A and B is the same - either A or B processing.

    PROCEDURE FOR TESTING: The procedure is conceptually is straight forward. It

    can be done by hand for two dimensions and for a few domains and practically

    impossible for more than two variables.

    1 Identify input variables. 2 Identify variable which appear in domain defining predicates, such as control

    flow predicates.

    3 Interpret all domain predicates in terms of input variables. 4 For p binary predicates, there are at most 2p combinations of TRUE-FALSE

    values and therefore, at most 2p domains. Find the set of all non null domains.

    The result is a boolean expression in the predicates consisting a set of AND

    terms joined by OR's. For example ABC+DEF+GHI...... Where the capital

    letters denote predicates. Each product term is a set of linear inequality that

    defines a domain or a part of a multiply connected domains.

    5 Solve these inequalities to find all the extreme points of each domain using any of the linear programming methods.


    INTRODUCTION: o Recall that we defined integration testing as testing the correctness of the interface

    between two otherwise correct components.


    o Components A and B have been demonstrated to satisfy their component tests,

    and as part of the act of integrating them we want to investigate possible

    inconsistencies across their interface.

    o Interface between any two components is considered as a subroutine call.

    o We're looking for bugs in that "call" when we do interface testing.

    o Let's assume that the call sequence is correct and that there are no type


    o For a single variable, the domain span is the set of numbers between (and

    including) the smallest value and the largest value. For every input variable we

    want (at least): compatible domain spans and compatible closures (Compatible

    but need not be Equal).


    o The set of output values produced by a function is called the range of the

    function, in contrast with the domain, which is the set of input values over which

    the function is defined.

    o For most testing, our aim has been to specify input values and to predict and/or

    confirm output values that result from those inputs.

    o Interface testing requires that we select the output values of the calling routine i.e.

    caller's range must be compatible with the called routine's domain.

    o An interface test consists of exploring the correctness of the following mappings:

    caller domain --> caller range (caller unit test)

    caller range --> called domain (integration test)

    called domain --> called range (called unit test)

    CLOSURE COMPATIBILITY: o Assume that the caller's range and the called domain spans the same numbers - for

    example, 0 to 17.

    o Figure 4.16 shows the four ways in which the caller's range closure and the

    called's domain closure can agree.

    o The thick line means closed and the thin line means open. Figure 4.16 shows the

    four cases consisting of domains that are closed both on top (17) and bottom (0),

    open top and closed bottom, closed top and open bottom, and open top and


    Figure 4.16: Range / Domain Closure Compatibility.

    o Figure 4.17 shows the twelve different ways the caller and the called can disagree

    about closure. Not all of them are necessarily bugs. The four cases in which a


    caller boundary is open and the called is closed (marked with a "?") are probably

    not buggy. It means that the caller will not supply such values but the called can

    accept them.

    Figure 4.17: Equal-Span Range / Domain Compatibility Bugs.


    o Figure 4.18 shows three possibly harmless span incompatibilities.

    Figure 4.18: Harmless Range / Domain Span incompatibility bug (Caller

    Span is smaller than Called).

    o In all cases, the caller's range is a subset of the called's domain. That's not

    necessarily a bug.

    o The routine is used by many callers; some require values inside a range and some

    don't. This kind of span incompatibility is a bug only if the caller expects the

    called routine to validate the called number for the caller.

    o Figure 4.19a shows the opposite situation, in which the called routine's domain

    has a smaller span than the caller expects. All of these examples are buggy.


    Figure 4.19: Buggy Range / Domain Mismatches

    o In Figure 4.19b the ranges and domains don't line up; hence good values are

    rejected, bad values are accepted, and if the called routine isn't robust enough, we

    have crashes.

    o Figure 4.19c combines these notions to show various ways we can have holes in

    the domain: these are all probably buggy.


    o For interface testing, bugs are more likely to concern single variables rather than

    peculiar combinations of two or more variables.

    o Test every input variable independently of other input variables to confirm

    compatibility of the caller's range and the called routine's domain span and

    closure of every domain defined for that variable.

    o There are two boundaries to test and it's a one-dimensional domain; therefore, it

    requires one on and one off point per boundary or a total of two on points and two

    off points for the domain - pick the off points appropriate to the closure


    o Start with the called routine's domains and generate test points in accordance to

    the domain-testing strategy used for that routine in component testing.

    o Unless you're a mathematical whiz you won't be able to do this without tools for

    more than one variable at a time.






    o Flow graphs are being an abstract representation of programs.

    o Any question about a program can be cast into an equivalent question about an

    appropriate flowgraph.

    o Most software development, testing and debugging tools use flow graphs analysis


    PATH PRODUCTS: o Normally flow graphs used to denote only control flow connectivity.

    o The simplest weight we can give to a link is a name.

    o Using link names as weights, we then convert the graphical flow graph into an

    equivalent algebraic like expressions which denotes the set of all possible paths

    from entry to exit for the flow graph.

    o Every link of a graph can be given a name.

    o The link name will be denoted by lower case italic letters In tracing a path or path

    segment through a flow graph, you traverse a succession of link names.

    o The name of the path or path segment that corresponds to those links is expressed

    naturally by concatenating those link names.

    o For example, if you traverse links a,b,c and d along some path, the name for that

    path segment is abcd. This pa

    o th name is also called a path product. Figure 5.1 shows some examples:

    Figure 5.1: Examples of paths.


    PATH EXPRESSION: o Consider a pair of nodes in a graph and the set of paths between those node.

    o Denote that set of paths by Upper case letter such as X,Y. From Figure 5.1c, the

    members of the path set can be listed as follows:

    ac, abc, abbc, abbbc, abbbbc.............

    o Alternatively, the same set of paths can be denoted by :


    o The + sign is understood to mean "or" between the two nodes of interest, paths ac,

    or abc, or abbc, and so on can be taken.

    o Any expression that consists of path names and "OR"s and which denotes a set of

    paths between two nodes is called a "Path Expression.


    o The name of a path that consists of two successive path segments is conveniently

    expressed by the concatenation or Path Product of the segment names.

    o For example, if X and Y are defined as X=abcde,Y=fghij,then the path

    corresponding to X followed by Y is denoted by


    o Similarly,





    o If X and Y represent sets of paths or path expressions, their product represents the

    set of paths that can be obtained by following every element of X by any element

    of Y in all possible ways. For example,

    o X = abc + def + ghi

    o Y = uvw + z


    XY = abcuvw + defuvw + ghiuvw + abcz + defz + ghiz

    o If a link or segment name is repeated, that fact is denoted by an exponent. The

    exponent's value denotes the number of repetitions:

    o a1 = a; a

    2 = aa; a

    3 = aaa; a

    n = aaaa . . . n times.

    Similarly, if X = abcde then

    X1 = abcde

    X2 = abcdeabcde = (abcde)


    X3 = abcdeabcdeabcde = (abcde)


    = abcde(abcde)2 = (abcde)


    o The path product is not commutative (that is XY!=YX).

    o The path product is Associative.

    RULE 1: A(BC)=(AB)C=ABC

    where A,B,C are path names, set of path names or path expressions.


    o The zeroth power of a link name, path product, or path expression is also needed

    for completeness. It is denoted by the numeral "1" and denotes the "path" whose

    length is zero - that is, the path that doesn't have any links.

    o a0 = 1

    o X0 = 1

    PATH SUMS: o The "+" sign was used to denote the fact that path names were part of the same set

    of paths.

    o The "PATH SUM" denotes paths in parallel between nodes.

    o Links a and b in Figure 5.1a are parallel paths and are denoted by a + b. Similarly,

    links c and d are parallel paths between the next two nodes and are denoted by c +


    o The set of all paths between nodes 1 and 2 can be thought of as a set of parallel

    paths and denoted by eacf+eadf+ebcf+ebdf.

    o If X and Y are sets of paths that lie between the same pair of nodes, then X+Y

    denotes the UNION of those set of paths. For example, in Figure 5.2:

    Figure 5.2: Examples of path sums.

    The first set of parallel paths is denoted by X + Y + d and the second set by U + V

    + W + h + i + j. The set of all paths in this flowgraph is f(X + Y + d)g(U + V + W

    + h + i + j)k

    o The path is a set union operation, it is clearly Commutative and Associative.

    o RULE 2: X+Y=Y+X

    o RULE 3: (X+Y)+Z=X+(Y+Z)=X+Y+Z

    DISTRIBUTIVE LAWS: o The product and sum operations are distributive, and the ordinary rules of

    multiplication apply; that is

    RULE 4: A(B+C)=AB+AC and (B+C)D=BD+CD

    o Applying these rules to the below Figure 5.1a yields

    o e(a+b)(c+d)f=e(ac+ad+bc+bd)f = eacf+eadf+ebcf+ebdf


    o If X and Y denote the same set of paths, then the union of these sets is unchanged;


    RULE 5: X+X=X (Absorption Rule)

    o If a set consists of paths names and a member of that set is added to it, the "new"

    name, which is already in that set of names, contributes nothing and can be


    o For example,

    o if X=a+aa+abc+abcd+def then


    X+a = X+aa = X+abc = X+abcd = X+def = X

    It follows that any arbitrary sum of identical path expressions reduces to the same

    path expression.

    LOOPS: Loops can be understood as an infinite set of parallel paths. Say that the loop consists of

    a single link b. then the set of all paths through that loop point is


    Figure 5.3: Examples of path loops.

    This potentially infinite sum is denoted by b* for an individual link and by X*

    Figure 5.4: Another example of path loops.

    o The path expression for the above figure is denoted by the notation:


    o Evidently,

    aa*=a*a=a+ and XX*=X*X=X+

    o It is more convenient to denote the fact that a loop cannot be taken more than a

    certain, say n, number of times.

    o A bar is used under the exponent to denote the fact as follows:

    Xn = X








    RULES 6 - 16: o The following rules can be derived from the previous rules:

    o RULE 6: Xn + X

    m = X

    n if n>m

    RULE 6: Xn + X

    m = X

    m if m>n

    RULE 7: XnX

    m = X


    RULE 8: XnX

    * = X


    n = X


    RULE 9: XnX

    + = X


    n = X


    RULE 10: X*X

    + = X


    * = X


    RULE 11: 1 + 1 = 1

    RULE 12: 1X = X1 = X

    Following or preceding a set of paths by a path of zero length does not change the


    RULE 13: 1n = 1

    n = 1

    * = 1

    + = 1

    No matter how often you traverse a path of zero length,It is a path of zero length.

    RULE 14: 1++1 = 1


    The null set of paths is denoted by the numeral 0. it obeys the following rules:

    RULE 15: X+0=0+X=X

    RULE 16: 0X=X0=0


    If you block the paths of a graph for or aft by a graph that has no paths , there

    wont be any paths.



    o This section presents a reduction procedure for converting a flowgraph whose

    links are labeled with names into a path expression that denotes the set of all

    entry/exit paths in that flowgraph. The procedure is a node-by-node removal


    o The steps in Reduction Algorithm are as follows:

    1. Combine all serial links by multiplying their path expressions. 2. Combine all parallel links by adding their path expressions. 3. Remove all self-loops (from any node to itself) by replacing them with a

    link of the form X*, where X is the path expression of the link in that loop.

    STEPS 4 - 8 ARE IN THE ALGORIHTM'S LOOP: 4. Select any node for removal other than the initial or final node. Replace it

    with a set of equivalent links whose path expressions correspond to all the

    ways you can form a product of the set of inlinks with the set of outlinks

    of that node.

    5. Combine any remaining serial links by multiplying their path expressions. 6. Combine all parallel links by adding their path expressions. 7. Remove all self-loops as in step 3. 8. Does the graph consist of a single link between the entry node and the exit

    node? If yes, then the path expression for that link is a path expression for

    the original flowgraph; otherwise, return to step 4.

    o A flowgraph can have many equivalent path expressions between a given pair of

    nodes; that is, there are many different ways to generate the set of all paths

    between two nodes without affecting the content of that set.

    o The appearance of the path expression depends, in general, on the order in which

    nodes are removed.


    o The cross - term step is the fundamental step of the reduction algorithm.

    o It removes a node, thereby reducing the number of nodes by one.

    o Successive applications of this step eventually get you down to one entry and one

    exit node. The following diagram shows the situation at an arbitrary node that has

    been selected for removal:

    o From the above diagram, one can infer:

    o (a + b)(c + d + e) = ac + ad + + ae + bc + bd + be



    o There are two ways of looking at the loop-removal operation:

    o In the first way, we remove the self-loop and then multiply all outgoing links by


    o In the second way, we split the node into two equivalent nodes, call them A and

    A' and put in a link between them whose path expression is Z*. Then we remove

    node A' using steps 4 and 5 to yield outgoing links whose path expressions are

    Z*X and Z*Y.


    o Let us see by applying this algorithm to the following graph where we remove

    several nodes in order; that is

    Figure 5.5: Example Flowgraph for demonstrating reduction procedure.

    o Remove node 10 by applying step 4 and combine by step 5 to yield

    o Remove node 9 by applying step4 and 5 to yield


    o Remove node 7 by steps 4 and 5, as follows:

    o Remove node 8 by steps 4 and 5, to obtain:


    Removal of node 8 above led to a pair of parallel links between nodes 4 and 5. combine

    them to create a path expression for an equivalent link whose path expression is c+gkh;

    that is

    o LOOP TERM (STEP 7): Removing node 4 leads to a loop term. The graph has now been replaced with the

    following equivalent simpler graph:

    o Continue the process by applying the loop-removal step as follows:


    o Removing node 5 produces:

    o Remove the loop at node 6 to yield:

    o Remove node 3 to yield

    o Removing the loop and then node 6 result in the following expression:


    o You can practice by applying the algorithm on the following flowgraphs and

    generate their respective path expressions:

    Figure 5.6: Some graphs and their path expressions.



    o The purpose of the node removal algorithm is to present one very generalized concept-

    the path expression and way of getting it.

    o Every application follows this common pattern:

    1. Convert the program or graph into a path expression. 2. Identify a property of interest and derive an appropriate set of "arithmetic" rules

    that characterizes the property.

    Replace the link names by the link weights for the property of interest. The path expression has

    now been converted to an expression in some algebra, such as

    1. Ordinary algebra, regular expressions, or boolean algebra. This algebraic expression summarizes the property of interest over the set of all paths.

    2. Simplify or evaluate the resulting "algebraic" expression to answer the question you asked.

    HOW MANY PATHS IN A FLOW GRAPH ? o The question is not simple. Here are some ways you could ask it:

    1. What is the maximum number of different paths possible? 2. What is the fewest number of paths possible? 3. How many different paths are there really? 4. What is the average number of paths?

    o Determining the actual number of different paths is an inherently difficult

    problem because there could be unachievable paths resulting from correlated and

    dependent predicates.

    o If we know both of these numbers (maximum and minimum number of possible

    paths) we have a good idea of how complete our testing is.

    o Asking for "the average number of paths" is meaningless.


    o Label each link with a link weight that corresponds to the number of paths that

    link represents.

    o Also mark each loop with the maximum number of times that loop can be taken.

    If the answer is infinite, you might as well stop the analysis because it is clear that

    the maximum number of paths will be infinite.

    o There are three cases of interest: parallel links, serial links, and loops.

    o This arithmetic is an ordinary algebra. The weight is the number of paths in each



    o EXAMPLE:

    The following is a reasonably well-structured program.

    Each link represents a single link and consequently is given a weight of

    "1" to start. Lets say the outer loop will be taken exactly four times and

    inner Loop Can be taken zero or three times Its path expression, with a

    little work, is:

    Path expression: a(b+c)d{e(fi)*fgj(m+l)k}*e(fi)*fgh

    A: The flow graph should be annotated by replacing the link name with

    the maximum of paths through that link (1) and also note the number of

    times for looping.

    B: Combine the first pair of parallel loops outside the loop and also the

    pair in the outer loop.

    C: Multiply the things out and remove nodes to clear the clutter.

    1. For the Inner Loop: D:Calculate the total weight of inner loop, which can execute a min. of 0

    times and max. of 3 times. So, it inner loop can be evaluated as follows:

    13 = 1

    0 + 1

    1 + 1

    2 + 1

    3 = 1 + 1 + 1 + 1 = 4

    2. E: Multiply the link weights inside the loop: 1 X 4 = 4 3. F: Evaluate the loop by multiplying the link wieghts: 2 X 4 = 8. 4. G: Simpifying the loop further results in the total maximum number of

    paths in the flowgraph:

    2 X 84 X 2 = 32,768.


    Alternatively, you could have substituted a "1" for each link in the path expression and then

    simplified, as follows:

    a(b+c)d{e(fi)*fgj(m+l)k}*e(fi)*fgh = 1(1 + 1)1(1(1 x 1)

    31 x 1 x 1(1 + 1)1)

    41(1 x 1)

    31 x 1 x 1

    = 2(131 x (2))



    = 2(4 x 2)4 x 4

    = 2 x 84 x 4 = 32,768

    This is the same result we got graphically.Actually, the outer loop should be taken exactly four

    times. That doesn't mean it will be taken zero or four times. Consequently, there is a superfluous

    "4" on the outlink in the last step. Therefore the maximum number of different paths is 8192

    rather than 32,768.

    STRUCTURED FLOWGRAPH: Structured code can be defined in several different ways that do not involve ad-hoc rules such as

    not using GOTOs.

    A structured flowgraph is one that can be reduced to a single link by successive application of

    the transformations of Figure 5.7.


    Figure 5.7: Structured Flowgraph Transformations.

    The node-by-node reduction procedure can also be used as a test for structured code.Flow graphs

    that DO NOT contains one or more of the graphs shown below (Figure 5.8) as subgraphs are


    1. Jumping into loops 2. Jumping out of loops 3. Branching into decisions 4. Branching out of decisions

    Figure 5.8: Un-structured sub-graphs.



    A lower bound on the number of paths in a routine can be approximated for structured flow


    The arithmetic is as follows:

    The values of the weights are the number of members in a set of paths.

    EXAMPLE: Applying the arithmetic to the earlier example gives us the identical steps

    unitl step 3 (C) as below:

    From Step 4, the it would be different from the previous example:


    If you observe the original graph, it takes at least two paths to cover and

    that it can be done in two paths.

    If you have fewer paths in your test plan than this minimum you probably

    haven't covered. It's another check.

    CALCULATING THE PROBABILITY: Path selection should be biased toward the low - rather than the high-probability paths.This

    raises an interesting question:

    What is the probability of being at a certain point in a routine?

    This question can be answered under suitable assumptions primarily that all probabilities

    involved are independent, which is to say that all decisions are independent and uncorrelated.

    We use the same algorithm as before: node-by-node removal of uninteresting nodes.

    Weights, Notations and Arithmetic:

    Probabilities can come into the act only at decisions (including decisions

    associated with loops).

    Annotate each outlink with a weight equal to the probability of going in

    that direction.

    Evidently, the sum of the outlink probabilities must equal 1

    For a simple loop, if the loop will be taken a mean of N times, the looping

    probability is N/(N + 1) and the probability of not looping is 1/(N + 1).

    A link that is not part of a decision node has a probability of 1.

    The arithmetic rules are those of ordinary arithmetic.


    In this table, in case of a loop, PA is the probability of the link leaving the

    loop and PL is the probability of looping.

    The rules are those of ordinary probability theory.

    1. If you can do something either from column A with a probability of PA or from column B with a probability PB, then the probability

    that you do either is PA + PB.

    2. For the series case, if you must do both things, and their probabilities are independent (as assumed), then the probability

    that you do both is the product of their probabilities.

    For example, a loop node has a looping probability of PL and a probability

    of not looping of PA, which is obviously equal to I - PL.

    Following the above rule, all we've done is replace the outgoing

    probability with 1 - so why the complicated rule? After a few steps in

    which you've removed nodes, combined parallel terms, removed loops and

    the like, you might find something like this:

    because PL + PA + PB + PC = 1, 1 - PL = PA + PB + PC, and


    which is what we've postulated for any decision. In other words, division

    by 1 - PL renormalizes the outlink probabilities so that their sum equals

    unity after the loop is removed.

    EXAMPLE: Here is a complicated bit of logic. We want to know the probability

    associated with cases A, B, and C.

    Let us do this in three parts, starting with case A. Note that the sum of the

    probabilities at each decision node is equal to 1. Start by throwing away

    anything that isn't on the way to case A, and then apply the reduction

    procedure. To avoid clutter, we usually leave out probabilities equal to 1.

    CASE A:


    Case B is simpler:

    Case C is similar and should yield a probability of 1 - 0.125 - 0.158 =


    These checks. It's a good idea when doing this sort of thing to calculate all

    the probabilities and to verify that the sum of the routine's exit

    probabilities does equal 1.

    If it doesn't, then you've made calculation error or, more likely, you've left

    out some bra How about path probabilities? That's easy. Just trace the path

    of interest and multiply the probabilities as you go.

    Alternatively, write down the path name and do the indicated arithmetic



    Say that a path consisted of links a, b, c, d, e, and the associated

    probabilities were .2, .5, 1., .01, and I respectively. Path abcbcbcdeabddea

    would have a probability of 5 x 10-10


    Long paths are usually improbable.


    Given the execution time of all statements or instructions for every link in a flowgraph and the

    probability for each direction for all decisions are to find the mean processing time for the

    routine as a whole.

    The model has two weights associated with every link: the processing time for that link, denoted

    by T, and the probability of that link P.

    The arithmetic rules for calculating the mean time:

    EXAMPLE: 1. Start with the original flow graph annotated with probabilities and processing time.

    2.Combine the parallel links of the outer loop. The result is just the mean of the

    processing times for the links because there aren't any other links leaving the first

    node. Also combine the pair of links at the beginning of the flow graph.

    3. Combine as many serial links as you can.


    4. Use the cross-term step to eliminate a node and to create the inner self - loop.

    5.Finally, you can get the mean processing time, by using the arithmetic rules as follows:


    This model can be used to answer several different questions that can turn up in debugging.

    It can also help decide which test cases to design.

    The question is:

    Given a pair of complementary operations such as PUSH (the stack) and POP (the stack),

    considering the set of all possible paths through the routine, what is the net effect of the

    routine? PUSH or POP? How many times? Under what conditions? Here are some other examples of complementary operations to which this model applies: GET/RETURN a resource block. OPEN/CLOSE a file.

    START/STOP a device or process.

    EXAMPLE 1 (PUSH / POP): Here is the Push/Pop Arithmetic:


    The numeral 1 is used to indicate that nothing of interest (neither PUSH

    nor POP) occurs on a given link.

    "H" denotes PUSH and "P" denotes POP. The operations are

    commutative, associative, and distributive.

    Consider the following flow graph:

    P(P + 1)1{P(HH)

    n1HP1(P + H)1}



    Simplifying by using the arithmetic tables,

    = (P2 + P){P(HH)

    n1(P + H)}



    = (P2 + P){H


    2 + 1)}



    Below Table 5.9 shows several combinations of values for the two looping

    terms - M1 is the number of times the inner loop will be taken and M2 the

    number of times the outer loop will be taken.


    Figure 5.9: Result of the PUSH / POP Graph Analysis.

    These expressions state that the stack will be popped only if the inner loop

    is not taken.

    The stack will be left alone only if the inner loop is iterated once, but it

    may also be pushed.

    For all other values of the inner loop, the stack will only be pushed.

    EXAMPLE 2 (GET / RETURN): Exactly the same arithmetic tables used for previous example are used for

    GET / RETURN a buffer block or resource, or, in fact, for any pair of


    complementary operations in which the total number of operations in

    either direction is cumulative.

    The arithmetic tables for GET/RETURN are:

    "G" denotes GET and "R" denotes RETURN.

    Consider the following flowgraph:

    G(G + R)G(GR)*GGR*R

    = G(G + R)G3R*R

    = (G + R)G3R*

    = (G4 + G


    This expression specifies the conditions under which the resources will be

    balanced on leaving the routine.

    If the upper branch is taken at the first decision, the second loop must be

    taken four times.

    If the lower branch is taken at the first decision, the second loop must be

    taken twice.

    For any other values, the routine will not balance. Therefore, the first loop

    does not have to be instrumented to verify this behavior because its impact

    should be nil.


    o The main limitation to these applications is the problem of unachievable paths. o The node-by-node reduction procedure, and most graph-theory-based algorithms work

    well when all paths are possible, but may provide misleading results when some paths are


    o The approach to handling unachievable paths (for any application) is to partition the graph into subgraphs so that all paths in each of the subgraphs are achievable.

    o The resulting subgraphs may overlap, because one path may be common to several different subgraphs.

    o Each predicate's truth-functional value potentially splits the graph into two subgraphs. For n predicates, there could be as many as 2

    n subgraphs.



    THE PROBLEM: o The generic flow-anomaly detection problem (note: not just data-flow anomalies,

    but any flow anomaly) is that of looking for a specific sequence of options

    considering all possible paths through a routine.

    o Let the operations be SET and RESET, denoted by s and r respectively, and we

    want to know if there is a SET followed immediately a SET or a RESET followed

    immediately by a RESET (an ss or an rr sequence).

    o Some more application examples:

    1. A file can be opened (o), closed (c), read (r), or written (w). If the file is read or written to after it's been closed, the sequence is nonsensical.

    Therefore, cr and cw are anomalous. Similarly, if the file is read before it's

    been written, just after opening, we may have a bug. Therefore, or is also

    anomalous. Furthermore, oo and cc, though not actual bugs, are a waste of

    time and therefore should also be examined.

    2. A tape transport can do a rewind (d), fast-forward (f), read (r), write (w), stop (p), and skip (k). There are rules concerning the use of the transport;

    for example, you cannot go from rewind to fast-forward without an

    intervening stop or from rewind or fast-forward to read or write without an

    intervening stop. The following sequences are anomalous: df, dr, dw, fd,

    and fr. Does the flowgraph lead to anomalous sequences on any path? If

    so, what sequences and under what circumstances?

    3. The data-flow anomalies discussed in Unit 4 requires us to detect the dd, dk, kk, and ku sequences. Are there paths with anomalous data flows?

    THE METHOD: o Annotate each link in the graph with the appropriate operator or the null operator


    o Simplify things to the extent possible, using the fact that a + a = a and 12 = 1.

    o You now have a regular expression that denotes all the possible sequences of

    operators in that graph. You can now examine that regular expression for the

    sequences of interest.

    o EXAMPLE: Let A, B, C, be nonempty sets of character sequences whose

    smallest string is at least one character long. Let T be a two-character string of

    characters. Then if T is a substring of (i.e., if T appears within) ABnC, then T will

    appear in AB2C. (HUANG's Theorem)

    As an example, let

    o A = pp

    B = srr

    C = rp

    T = ss

    The theorem states that ss will appear in pp(srr)nrp if it appears in pp(srr)



    o However, let

    A = p + pp + ps

    B = psr + ps(r + ps)

    C = rp

    T = P4

    Is it obvious that there is a p4 sequence in AB

    nC? The theorem states that we have

    only to look at

    (p + pp + ps)[psr + ps(r + ps)]2rp

    Multiplying out the expression and simplifying shows that there is no p4


    o Incidentally, the above observation is an informal proof of the wisdom of looping

    twice discussed in Unit 2. Because data-flow anomalies are represented by two-

    character sequences, it follows the above theorem that looping twice is what you

    need to do to find such anomalies.


    o Huang's theorem can be easily generalized to cover sequences of greater length

    than two characters. Beyond three characters, though, things get complex and this

    method has probably reached its utilitarian limit for manual application.

    o There are some nice theorems for finding sequences that occur at the beginnings

    and ends of strings but no nice algorithms for finding strings buried in an


    o Static flow analysis methods can't determine whether a path is or is not

    achievable. Unless the flow analysis includes symbolic execution or similar

    techniques, the impact of unachievable paths will not be included in the analysis.

    The flow-anomaly application, for example, doesn't tell us that there will be a flow

    anomaly - it tells us that if the path is achievable, then there will be a flow anomaly. Such

    analytical problems go away, of course, if you take the trouble to design routines for

    which all paths are achievable.




    o The functional requirements of many programs can be specified by decision

    tables, which provide a useful basis for program and test design.

    o Consistency and completeness can be analyzed by using boolean algebra, which

    can also be used as a basis for test design. Boolean algebra is trivialized by using

    Karnaugh-Veitch charts.


    o "Logic" is one of the most often used words in programmers' vocabularies but one

    of their least used techniques.

    o Boolean algebra is to logic as arithmetic is to mathematics. Without it, the tester

    or programmer is cut off from many test and design techniques and tools that

    incorporate those techniques.

    o Logic has been, for several decades, the primary tool of hardware logic designers.

    o Many test methods developed for hardware logic can be adapted to software logic

    testing. Because hardware testing automation is 10 to 15 years ahead of software

    testing automation, hardware testing methods and its associated theory is a fertile

    ground for software testing methods.

    o As programming and test techniques have improved, the bugs have shifted closer

    to the process front end, to requirements and their specifications. These bugs

    range from 8% to 30% of the total and because they're first-in and last-out, they're

    the costliest of all.

    o The trouble with specifications is that they're hard to express.

    o Boolean algebra (also known as the sentential calculus) is the most basic of all

    logic systems.

    o Higher-order logic systems are needed and used for formal specifications.

    o Much of logical analysis can be and is embedded in tools. But these tools

    incorporate methods to simplify, transform, and check specifications, and the

    methods are to a large extent based on boolean algebra.


    The knowledge-based system (also expert system, or "artificial

    intelligence" system) has become the programming construct of choice for

    many applications that were once considered very difficult.

    Knowledge-based systems incorporate knowledge from a knowledge

    domain such as medicine, law, or civil engineering into a database. The

    data can then be queried and interacted with to provide solutions to

    problems in that domain.

    One implementation of knowledge-based systems is to incorporate the

    expert's knowledge into a set of rules. The user can then provide data and

    ask questions based on that data.

    The user's data is processed through the rule base to yield conclusions

    (tentative or definite) and requests for more data. The processing is done

    by a program called the inference engine.

    Understanding knowledge-based systems and their validation problems

    requires an understanding of formal logic.

    o Decision tables are extensively used in business data processing; Decision-table

    preprocessors as extensions to COBOL are in common use; boolean algebra is

    embedded in the implementation of these processors.

    o Although programmed tools are nice to have, most of the benefits of boolean

    algebra can be reaped by wholly manual means if you have the right conceptual

    tool: the Karnaugh-Veitch diagram is that conceptual tool.



    Figure 6.1 is a limited - entry decision table. It consists of four areas called the condition

    stub, the condition entry, the action stub, and the action entry.

    Each column of the table is a rule that specifies the conditions under which the actions

    named in the action stub will take place.

    The condition stub is a list of names of conditions.

    Figure 6.1 : Examples of Decision Table.

    A more general decision table can be as below:

    Figure 6.2 : Another Examples of Decision Table.

    A rule specifies whether a condition should or should not be met for the rule to be

    satisfied. "YES" means that the condition must be met, "NO" means that the condition

    must not be met, and "I" means that the condition plays no part in the rule, or it is

    immaterial to that rule.

    The action stub names the actions the routine will take or initiate if the rule is satisfied.

    If the action entry is "YES", the action will take place; if "NO", the action will not take


    The table in Figure 6.1 can be translated as follows:

    Action 1 will take place if conditions 1 and 2 are met and if conditions 3 and 4 are not met (rule

    1) or if conditions 1, 3, and 4 are met (rule 2).

    "Condition" is another word for predicate.


    Decision-table uses "condition" and "satisfied" or "met". Let us use "predicate" and


    Now the above translations become:

    1. Action 1 will be taken if predicates 1 and 2 are true and if predicates 3 and 4 are false (rule 1), or if predicates 1, 3, and 4 are true (rule 2).

    2. Action 2 will be taken if the predicates are all false, (rule 3). 3. Action 3 will take place if predicate 1 is false and predicate 4 is true (rule 4).

    In addition to the stated rules, we also need a Default Rule that specifies the default

    action to be taken when all other rules fail. The default rules for Table in Figure 6.1 is

    shown in Figure 6.3

    Figure 6.3 : The default rules of Table in Figure 6.1


    o Decision tables can be automatically translated into code and, as such, are a

    higher-order language

    o If the rule is satisfied, the corresponding action takes place

    o Otherwise, rule 2 is tried. This process continues until either a satisfied rule

    results in an action or no rule is satisfied and the default action is taken

    o Decision tables have become a useful tool in the programmers kit, in business

    data processing.


    1. The specification is given as a decision table or can be easily converted into one. 2. The order in which the predicates are evaluated does not affect interpretation of the

    rules or the resulting action - i.e., an arbitrary permutation of the predicate order

    will not, or should not, affect which action takes place.

    3. The order in which the rules are evaluated does not affect the resulting action - i.e., an arbitrary permutation of rules will not, or should not, affect which action takes


    4. Once a rule is satisfied and an action selected, no other rule need be examined. 5. If several actions can result from satisfying a rule, the order in which the actions

    are executed doesn't matter.



    o Decision tables can also be used to examine a program's structure.

    o Figure 6.4 shows a program segment that consists of a decision tree.

    o These decisions, in various combinations, can lead to actions 1, 2, or 3.

    Figure 6.4 : A Sample Program

    o If the decision appears on a path, put in a YES or NO as appropriate. If the

    decision does not appear on the path, put in an I, Rule 1 does not contain decision

    C, therefore its entries are: YES, YES, I, YES.

    o The corresponding decision table is shown in Table 6.1













































    ACTION 1

    ACTION 2

    ACTION 3



















    Table 6.1: Decision Table corresponding to Figure 6.4

    As an example, expanding the immaterial cases results as below:


    Table 6.2: Expansion of Table 6.1

    o Similalrly, If we expand the immaterial cases for the above Table 6.1, it results in

    Table 6.2 as below:

    R 1 RULE 2 R 3 RULE 4 R 5 R 6





























    1. Sixteen cases are represented in Table 6.1, and no case appears twice. 2. Consequently, the flowgraph appears to be complete and consistent. 3. As a first check, before you look for all sixteen combinations, count the number

    of Y's and N's in each row. They should be equal. We can find the bug that way.


    1. Consider the following specification whose putative flowgraph is shown in Figure 6.5:

    1. If condition A is met, do process A1 no matter what other actions are taken or what other conditions are met.

    2. If condition B is met, do process A2 no matter what other actions are taken or what other conditions are met.

    3. If condition C is met, do process A3 no matter what other actions are taken or what other conditions are met.

    4. If none of the conditions is met, then do processes A1, A2, and A3. 5. When more than one process is done, process A1 must be done first, then

    A2, and then A3. The only permissible cases are: (A1), (A2), (A3),

    (A1,A3), (A2,A3) and (A1,A2,A3).

    2. Figure 6.5 shows a sample program with a bug.


    Figure 6.5 : A Troublesome Program

    o The programmer tried to force all three processes to be executed for the

    cases but forgot that the B and C predicates would be done again, thereby

    bypassing processes A2 and A3.

    o Table 6.3 shows the conversion of this flow graph into a decision table after


    Table 6.3: Decision Table for Figure 6.5



    o Logic-based testing is structural testing when it's applied to structure (e.g., control

    flow graph of an implementation); it's functional testing when it's applied to a


    o In logic-based testing we focus on the truth values of control flow predicates.

    o A predicate is implemented as a process whose outcome is a truth-functional


    o For our purpose, logic-based testing is restricted to binary predicates.

    o We start by generating path expressions by path tracing as in Unit V, but this

    time, our purpose is to convert the path expressions into boolean algebra, using

    the predicates' truth values (e.g., A and ) as weights.



    o STEPS: 1. Label each decision with an uppercase letter that represents the truth value

    of the predicate. The YES or TRUE branch is labeled with a letter (say A)

    and the NO or FALSE branch with the same letter overscored (say ).

    2. The truth value of a path is the product of the individual labels. Concatenation or products mean "AND". For example, the straight-

    through path of Figure 6.5, which goes via nodes 3, 6, 7, 8, 10, 11, 12, and

    2, has a truth value of ABC. The path via nodes 3, 6, 7, 9 and 2 has a value

    of .

    3. If two or more paths merge at a node, the fact is expressed by use of a plus sign (+) which means "OR".

    Figure 6.5: A Troublesome Program

    o Using this convention, the truth-functional values for several of the nodes can be

    expressed in terms of segments from previous nodes. Use the node name to

    identify the point.

    o There are only two numbers in boolean algebra: zero (0) and one (1). One means

    "always true" and zero means "always false".


    Boolean algebra has three operators: X (AND), + (OR) and (NOT)

    X : meaning AND. Also called multiplication. A statement such as AB (A

    X B) means "A and B are both true". This symbol is usually left out as in

    ordinary algebra.

    + : meaning OR. "A + B" means "either A is true or B is true or both".


    meaning NOT. Also negation or complementation. This is read as either

    "not A" or "A bar". The entire expression under the bar is negated.

    The following are the laws of boolean algebra:

    In all of the above, a letter can represent a single sentence or an entire boolean algebra


    Individual letters in a boolean algebra expression are called Literals (e.g. A,B)

    The product of several literals is called a product term (e.g., ABC, DE).

    An arbitrary boolean expression that has been multiplied out so that it consists of the sum of

    products (e.g., ABC + DEF + GH) is said to be in sum-of-products form.

    The result of simplifications (using the rules above) is again in the sum of product form and each

    product term in such a simplified version is called a prime implicant. For example, ABC + AB

    + DEF reduce by rule 20 to AB + DEF; that is, AB and DEF are prime implicants.

    The path expressions of Figure 6.5 can now be simplified by applying the rules.

    The following are the laws of boolean algebra:



    The deviation from the specification is now clear. The functions should have been:

    Loops complicate things because we may have to solve a boolean equation to determine what

    predicate value combinations lead to where.



    o If you had to deal with expressions in four, five, or six variables, you could get

    bogged down in the algebra and make as many errors in designing test cases as

    there are bugs in the routine you're testing.

    o Karnaugh-Veitch chart reduces boolean algebraic manipulations to graphical


    o Beyond six variables these diagrams get cumbersome and may not be effective.

    SINGLE VARIABLE: o Figure 6.6 shows all the boolean functions of a single variable and their

    equivalent representation as a KV chart.

    o The charts show all possible truth values that the variable A can have.

    o A "1" means the variables value is "1" or TRUE. A "0" means that the variable's

    value is 0 or FALSE.

    o The entry in the box (0 or 1) specifies whether the function that the chart

    represents is true or false for that value of the variable.

    o We usually do not explicitly put in 0 entries but specify only the conditions under

    which the function is true.


    Figure 6.6 : KV Charts for Functions of a Single Variable.

    TWO VARIABLES: o Figure 6.7 shows eight of the sixteen possible functions of two variables.

    o Each box corresponds to the combination of values of the variables for the row

    and column of that box.

    o A pair may be adjacent either horizontally or vertically but not diagonally.

    o Any variable that changes in either the horizontal or vertical direction does not

    appear in the expression.

    o In the fifth chart, the B variable changes from 0 to 1 going down the column, and

    because the A variable's value for the column is 1, the chart is equivalent to a

    simple A.


    Figure 6.7: KV Charts for Functions of Two Variables.

    o Figure 6.8 shows the remaining eight functions of two variables.

    o The first chart has two 1's in it, but because they are not adjacent, each must be

    taken separately.

    o They are written using a plus sign.

    o It is clear now why there are sixteen functions of two variables.

    o Each box in the KV chart corresponds to a combination of the variables' values.

    o That combination might or might not be in the function (i.e., the box

    corresponding to that combination might have a 1 or 0 entry).

    o Since n variables lead to 2n combinations of 0 and 1 for the variables, and each

    such combination (box) can be filled or not filled, leading to 22n

    ways of doing



    Figure 6.8: More Functions of Two Variables.

    o Consequently for one variable there are 221

    = 4 functions, 16 functions of 2

    variables, 256 functions of 3 variables, 16,384 functions of 4 variables, and so on.

    o Given two charts over the same variables, arranged the same way, their product is

    the term by term product, their sum is the term by term sum, and the negation of a

    chart is gotten by reversing all the 0 and 1 entries in the chart.




    o KV charts for three variables are shown below.

    o As before, each box represents an elementary term of three variables with a bar

    appearing or not appearing according to whether the row-column heading for that

    box is 0 or 1.

    o A three-variable chart can have groupings of 1, 2, 4, and 8 boxes.

    o A few examples will illustrate the principles:


    Figure 6.8: KV Charts for Functions of Three Variables.

    o You'll notice that there are several ways to circle the boxes into maximum-sized

    covering groups.


    UNIT V



    The finite state machine is as fundamental to software engineering as boolean algebra to logic.

    State testing strategies are based on the use of finite state machine models for software structure, software behavior, or specifications of software behavior.

    Finite state machines can also be implemented as table-driven software, in which case they are a powerful design option.

    State Graphs

    A state is defined as: A combination of circumstances or attributes belonging for the time being to a person or thing.

    For example, a moving automobile whose engine is running can have the following states with respect to its transmission.

    Reverse gear Neutral gear First gear Second gear Third gear Fourth gear

    State graph - Example

    For example, a program that detects the character sequence ZCZC can be in the following states.

    Neither ZCZC nor any part of it has been detected. Z has been detected. ZC has been detected. ZCZ has been detected. ZCZC has been detected.

    States are represented by Nodes. State are numbered or may identified by words

    or whatever else is convenient.

    Inputs and Transitions

    Whatever is being modeled is subjected to inputs. As a result of those inputs, the state changes, or is said to have made a Transition.

    Transitions are denoted by links that join the states.

    The input that causes the transition are marked on the link; that is, the inputs are link weights.

    There is one out link from every state for every input.


    If several inputs in a state cause a transition to the same subsequent state, instead of drawing a bunch of parallel links we can abbreviate the notation by listing the several

    inputs as in: input1, input2, input3.

    Finite State Machine

    A finite state machine is an abstract device that can be represented by a state graph having a finite number of states and a finite number of transitions between states.

    o Outputs

    An output can be associated with any link.

    Out puts are denoted by letters or words and are separated from inputs by a slash as follows: input/output.

    As always, output denotes anything of interest thats observable and is not restricted to explicit outputs by devices.

    Outputs are also link weights.

    If every input associated with a transition causes the same output, then denoted it as: o input1, input2, input3../output

    State Tables

    Big state graphs are cluttered and hard to follow.

    Its more convenient to represent the state graph as a table (the state table or state transition table) that specifies the states, the inputs, the transitions and

    the outputs.

    The following conventions are used:

    Each row of the table corresponds to a state.

    Each column corresponds to an input condition.

    The box at the intersection of a row and a column specifies the next state (the transition) and the output, if any.

    State Table-Example


    Time Versus Sequence

    State graphs dont represent time-they represent sequence.

    A transition might take microseconds or centuries;

    A system could be in one state for milliseconds and another for years- the state graph would be the same because it has no notion of time.

    Although the finite state machines model can be elaborated to include notions of time in addition to sequence, such as time Petri Nets.

    o Software implementation

    There is rarely a direct correspondence between programs and the behavior of a process described as a state graph.

    The state graph represents, the total behavior consisting of the transport, the software, the executive, the status returns, interrupts, and so on.

    There is no simple correspondence between lines of code and states. The state table forms the basis.

    Good State Graphs and Bad

    What constitutes a good or a bad state graph is to some extent biased by the kinds of state graphs that are likely to be used in a software test design context.

    Here are some principles for judging. o The total number of states is equal to the product of the possibilities of factors that

    make up the state.

    o For every state and input there is exactly one transition specified to exactly one, possibly the same, state.

    o For every transition there is one output action specified. The output could be trivial, but at least one output does something sensible.

    o For every state there is a sequence of inputs that will drive the system back to the same state.

    Important graphs

    State Bugs-Number of States

    The number of states in a state graph is the number of states we choose to recognize or model.


    The state is directly or indirectly recorded as a combination of values of variables that appear in the data base.

    For example, the state could be composed of the value of a counter whose possible values ranged from 0 to 9, combined with the setting of two bit flags, leading to a total of

    2*2*10=40 states.

    The number of states can be computed as follows: o Identify all the component factors of the state. o Identify all the allowable values for each factor. o The number of states is the product of the number of allowable values of all the


    Before you do anything else, before you consider one test case, discuss the number of states you think there are with the number of states the programmer thinks there are.

    There is no point in designing tests intended to check the systems behavior in various states if theres no agreement on how many states there are.

    o Impossible States

    Some times some combinations of factors may appear to be impossible.

    The discrepancy between the programmers state count and the testers state count is often due to a difference of opinion concerning impossible states.

    A robust piece of software will not ignore impossible states but will recognize them and invoke an illogical condition handler when they appear to have occurred.

    Equivalent States

    Two states are Equivalent if every sequence of inputs starting from one state produces exactly the same sequence of outputs when started from the other state. This notion can

    also be extended to set of states.

    Merging of Equivalent States


    Recognizing Equivalent States

    Equivalent states can be recognized by the following procedures:

    The rows corresponding to the two states are identical with respect to input/output/next state but the name of the next state could differ.

    There are two sets of rows which, except for the state names, have identical state graphs with respect to transitions and outputs. The two sets can be merged.


    unspecified and contradictory Transitions

    Every input-state combination must have a specified transition.

    If the transition is impossible, then there must be a mechanism that prevents the input from occurring in that state.

    Exactly one transition must be specified for every combination of input and state.

    A program cant have contradictions or ambiguities.

    Ambiguities are impossible because the program will do something for every input. Even the state does not change, by definition this is a transition to the same state.

    Unreachable States

    An unreachable state is like unreachable code.

    A state that no input sequence can reach.

    An unreachable state is not impossible, just as unreachable code is not impossible

    There may be transitions from unreachable state to other states; there usually because the state became unreachable as a result of incorrect transition.

    There are two possibilities for unreachable states: o There is a bug; that is some transitions are missing. o The transitions are there, but you dont know about it.

    Dead States

    A dead state is a state that once entered cannot be left.

    This is not necessarily a bug but it is suspicious.

    Output Errors

    The states, transitions, and the inputs could be correct, there could be no dead or unreachable states, but the output for the transition could be incorrect.

    Output actions must be verified independently of states and transitions. State Testing

    Impact of Bugs

    If a routine is specified as a state graph that has been verified as correct in all details. Program code or table or a combination of both must still be implemented.

    A bug can manifest itself as one of the following symptoms:

    Wrong number of states.

    Wrong transitions for a given state-input combination.

    Wrong output for a given transition.

    Pairs of states or sets of states that are inadvertently made equivalent.

    States or set of states that are split to create in equivalent duplicates.


    States or sets of states that have become dead.

    States or sets of states that have become unreachable.

    Principles of State Testing

    The strategy for state testing is analogous to that used for path testing flow graphs.

    Just as its impractical to go through every possible path in a flow graph, its impractical to go through every path in a state graph.

    The notion of coverage is identical to that used for flow graphs.

    Even though more state testing is done as a single case in a grand tour, its impractical to do it that way for several reasons.

    In the early phases of testing, you will never complete the grand tour because of bugs.

    Later, in maintenance, testing objectives are understood, and only a few of the states and transitions have to be tested. A grand tour is waste of time.

    Theirs is no much history in a long test sequence and so much has happened that verification is difficult.

    Starting point of state testing

    Define a set of covering input sequences that get back to the initial state when starting from the initial state.

    For each step in each input sequence, define the expected next state, the expected transition, and the expected output code.

    A set of tests, then, consists of three sets of sequences: o Input sequences o Corresponding transitions or next-state names o Output sequences

    Limitations and Extensions

    State transition coverage in a state graph model does not guarantee complete testing.

    How defines a hierarchy of paths and methods for combining paths to produce covers of state graphs.

    The simplest is called a 0 switch which corresponds to testing each transition individually.

    The next level consists of testing transitions sequences consisting of two transitions called 1 switches.

    The maximum length switch is n-1 switch where there are n numbers of states. o Situations at which state testing is useful

    Any processing where the output is based on the occurrence of one or more sequences of events, such as detection of specified input sequences, sequential format validation,

    parsing, and other situations in which the order of inputs is important.

    Most protocols between systems, between humans and machines, between components of a system.

    Device drivers such as for tapes and discs that have complicated retry and recovery procedures if the action depends on the state.

    Whenever a feature is directly and explicitly implemented as one or more state transition tables.



    Problem with Pictorial Graphs

    Graphs were introduced as an abstraction of software structure.

    Whenever a graph is used as a model, sooner or later we trace paths through it- to find a set of covering paths, a set of values that will sensitize paths, the logic function that controls the flow, the processing time of the routine, the equations that define the domain, or whether a state is

    reachable or not.

    Path is not easy, and its subject to error. You can miss a link here and there or cover some links twice.

    One solution to this problem is to represent the graph as a matrix and to use matrix operations equivalent to path tracing. These methods are more methodical and mechanical and dont depend

    on your ability to see a path they are more reliable.

    Tool Building If you build test tools or want to know how they work, sooner or later you will be implementing

    or investigating analysis routines based on these methods.

    It is hard to build algorithms over visual graphs so the properties or graph matrices are fundamental to tool building.

    The Basic Algorithms

    The basic tool kit consists of:

    Matrix multiplication, which is used to get the path expression from every node to every other node.

    A partitioning algorithm for converting graphs with loops into loop free graphs or equivalence classes.

    A collapsing process which gets the path expression from any node to any other node.

    The Matrix of a Graph A graph matrix is a square array with one row and one column for every node in the graph.

    Each row-column combination corresponds to a relation between the node corresponding to the row and the node corresponding to the column.

    The relation for example, could be as simple as the link name, if there is a link between the nodes.

    Some of the things to be observed:

    The size of the matrix equals the number of nodes.

    There is a place to put every possible direct connection or link between any and any other node.

    The entry at a row and column intersection is the link weight of the link that connects the two nodes in that direction.

    A connection from node i to j does not imply a connection from node j to node i.

    If there are several links between two nodes, then the entry is a sum; the + sign denotes parallel links as usual.


    A simple weight

    A simplest weight we can use is to note that there is or isnt a connection. Let 1 mean that there is a connection and 0 mean that there isnt.

    The arithmetic rules are: 1+1=1 1*1=1 1+0=1 1*0=0 0+0=0 0*0=0 A matrix defined like this is called connection matrix.

    Connection matrix The connection matrix is obtained by replacing each entry with 1 if there is a link and 0 if there


    As usual we dont write down 0 entries to reduce the clutter.


    Connection Matrix-continued

    Each row of a matrix denotes the out links of the node corresponding to that row.

    Each column denotes the in links corresponding to that node.

    A branch is a node with more than one nonzero entry in its row.

    A junction is node with more than one nonzero entry in its column.

    A self loop is an entry along the diagonal.

    Cyclomatic Complexity The cyclomatic complexity obtained by subtracting 1 from the total number of entries in each row

    and ignoring rows with no entries, we obtain the equivalent number of decisions for each row.

    Adding these values and then adding 1 to the sum yields the graphs cyclomatic complexity.



    A relation is a property that exists between two objects of interest.

    For example,

    Node a is connected to node b or aRb where R means is connected to.

    a>=b or aRb where R means greater than or equal.

    A graph consists of set of abstract objects called nodes and a relation R between the nodes.

    If aRb, which is to say that a has the relation R to b, it is denoted by a link from a to b.

    For some relations we can associate properties called as link weights.

    Transitive Relations

    A relation is transitive if aRb and bRc implies aRc.

    Most relations used in testing are transitive.

    Examples of transitive relations include: is connected to, is greater than or equal to, is less than or equal to, is a relative of, is faster than, is slower than, takes more time than, is a subset of,

    includes, shadows, is the boss of.

    Examples of intransitive relations include: is acquainted with, is a friend of, is a neighbor of, is lied to, has a du chain between.

    Reflexive Relations

    A relation R is reflexive if, for every a, aRa.

    A reflexive relation is equivalent to a self loop at every node.

    Examples of reflexive relations include: equals, is acquainted with, is a relative of.

    Examples of irreflexive relations include: not equals, is a friend of, is on top of, is under.

    Symmetric Relations

    A relation R is symmetric if for every a and b, aRb implies bRa.

    A symmetric relation mean that if there is a link from a to b then there is also a link from b to a.

    A graph whose relations are not symmetric are called directed graph.


    A graph over a symmetric relation is called an undirected graph.

    The matrix of an undirected graph is symmetric (aij=aji) for all i,j)

    Antisymmetric Relations

    A relation R is antisymmetric if for every a and b, if aRb and bRa, then a=b, or they are the same elements.

    Examples of antisymmetric relations: is greater than or equal to, is a subset of, time.

    Examples of nonantisymmetric relations: is connected to, can be reached from, is greater than, is a relative of, is a friend of

    quivalence Relations

    An equivalence relation is a relation that satisfies the reflexive, transitive, and symmetric properties.

    Equality is the most familiar example of an equivalence relation.

    If a set of objects satisfy an equivalence relation, we say that they form an equivalence class over that relation.

    The importance of equivalence classes and relations is that any member of the equivalence class is, with respect to the relation, equivalent to any other member of that class.

    The idea behind partition testing strategies such as domain testing and path testing, is that we can partition the input space into equivalence classes.

    Testing any member of the equivalence class is as effective as testing them all.

    Partial Ordering Relations

    A partial ordering relation satisfies the reflexive, transitive, and antisymmetric properties.

    Partial ordered graphs have several important properties: they are loop free, there is at least one maximum element, and there is at least one minimum element.

    The Powers of a Matrix

    Each entry in the graphs matrix expresses a relation between the pair of nodes that corresponds to that entry.

    Squaring the matrix yields a new matrix that expresses the relation between each pair of nodes via one intermediate node under the assumption that the relation is transitive.

    The square of the matrix represents all path segments two links long.

    The third power represents all path segments three links long.


    Matrix Powers and Products

    Given a matrix whose entries are aij, the square of that matrix is obtained by replacing every entry with


    aij= aik akj


    more generally, given two matrices A and B with entries aik and bkj, respectively, their product is a new matrix C, whose entries are cij, where:


    Cij= aik bkj


    Partitioning Algorithm

    Consider any graph over a transitive relation. The graph may have loops.

    We would like to partition the graph by grouping nodes in such a way that every loop is contained within one group or another.

    Such a graph is partially ordered.

    There are many used for an algorithm that does that:

    We might want to embed the loops within a subroutine so as to have a resulting graph which is loop free at the top level.

    Many graphs with loops are easy to analyze if you know where to break the loops.

    While you and I can recognize loops, its much harder to program a tool to do it unless you have a solid algorithm on which to base the tool.

    Node Reduction Algorithm (General)

    The matrix powers usually tell us more than we want to know about most graphs.

    In the context of testing, we usually interested in establishing a relation between two nodes-typically the entry and exit nodes.

    In a debugging context it is unlikely that we would want to know the path expression between every node and every other node.

    The advantage of matrix reduction method is that it is more methodical than the graphical method called as node by node removal algorithm.

    1. Select a node for removal; replace the node by equivalent links that bypass that node and add those links to the links they parallel.

    2. Combine the parallel terms and simplify as you can.

    3. Observe loop terms and adjust the out links of every node that had a self loop to account for the effect of the loop.

    4. The result is a matrix whose size has been reduced by 1. Continue until only the two nodes of interest exist.


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