Measuring the effectiveness of a test case

This work is concerned with the effectiveness of test cases used in program testing. It is well known that no matter which test-case selection method is used in program testing, some programming errors can still escape detection because the program may produce fortuitously correct results. One reason why a program may produce a fortuitously correct result is that it contains expressions of the form exp₁ op exp₂, and the test case used causes exp₁ to assume a special value such that exp₁ op exp₂=exp₁ regardless of the value of exp₂ . In that event, if there is an error in exp₂, it will never be reflected in the test result