What is Gray Box Testing?

Gray Box Testing is a software testing technique in which the tester validates the functions of the system with only a partial knowledge of its internal working.

This testing is a combination of both White Box and Black Box Testing, thereby achieving a better test coverage by validating the output of every function with the knowledge of how data flows through the internal nodes.

Importance of Gray Box Testing

This question is frequently asked by software teams. Why does Gray Box Testing have the advantage over White Box Testing and Black Box Testing? The answer is simple; it combines the advantages of both Black Box and White Box testing to achieve a wider test coverage.

Therefore, you can say that Gray Box Testing allows the validation of both the UI, as well as business layers of the application. This testing technique is primarily used in integration testing.

As an example, while testing some links on a website and finding them not working, the browser console can be opened to find the element and then the HTML edited, to test this issue on the fly. Gray Box testing also helps in nonfunctional testing and performance testing for example, since it makes it possible to navigate through different nodes of the application, thus making it possible for you to discover any performance bottlenecks on the go.

In another example, a web form is tested by proving that when entering a valid email ID and clicking submit, an email will be sent to the email ID entered. A black box tester will test this scenario by entering both valid and invalid email IDs and observing how the system behaves. But in the case of Gray Box testing, the tester might have some idea how this validation works. They know that the validation of this email is performed using Javascript on the client side, so it is easy to add another test case to disable javascript on the browser and run the test again. Being aware of the client side validation has allowed the tester to add an extra test case to their test suite, defining them as a Gray Box Tester.

Gray box testing

Gray Box Testing Methods

As discussed above, Gray Box Testing requires only a partial knowledge of the internal structure of the application. Therefore, tests can be designed using workflow diagrams, application algorithm, architecture diagrams, internal states of the application, and high-level specification. Below are different testing methods employed by Gray Box testing.

Techniques used in Gray Box Testing

  • Orthogonal Array Testing or OAT: This technique gives maximum test coverage with the minimum number of test cases. It is used as a subset of all possible combinations.
  • Matrix Testing: In this technique, all variables defined in the applications can be tabulated and tested against the requirements. This testing technique states the standing report of the application under development.
  • Pattern Testing: Here testing is done based on the history of failures on the application. Ultimately, this validates the quality of the application against the design and plan.
  • Regression Testing: The application tests for any changes in code compared to the previous version, so a set of test cases will be run here. The test strategy would be to either run all the test cases, run test cases in a specific area or to test some risk-based test cases to cover the most important aspects of the application.

Disadvantages of Gray Box Testing

  • Since the knowledge of code is limited to the tester, the ability to analyze each node of the application is limited.
  • If there is enough unit test coverage around the modules where the Gray box testing is planned, then the testing becomes redundant.
  • With limited White Box knowledge, testing of every path will be practically impossible, so some paths may go untested.


Gray Box Testing reduces the overall cost of the project because bugs can be discovered very early and efficiently. It also helps in GUI testing, performance testing, security testing and Integration testing, thereby validating the quality of different attributes early in the life cycle of a project.


Jithin Nair
