Mutation testing is testing where our goal is to make mutant software fail, and thus demonstrate the adequacy of our test case. How do we perform mutation testing?

Step one: We create a set of mutant software. In other words, each mutant software differs from the original software by one mutation, i.e. one single syntax change made to one of its program statements, i.e. each mutant software contains one single fault.

Step two: We write and apply test cases to the original software and to the mutant software.

Step three: We evaluate the results, based on the following set of criteria: Our test case is inadequate, if both the original software and all mutant software generate the same output. Our test case is adequate, if our test case detects faults in our software, or, if, at least, one mutant software generates a different output than does the original software for our test case.