an automatic test generation system in which the coverage levels of the tests can be controlled to tradeoff between the extent of the test conducted and the length of time required to execute the test . the system under test is modeled as an extended finite state machine made up of interconnected models . the coverage level of each model can be controlled to avoid generating paths that differ only be edges within certain models if those differing edges are already included in other paths . the coverage level for each model can be set automatically through a process which computes the effect on the total number of paths generated when the coverage level of selected models is varied .