Test Quality

Use Mutation Testing to Find Weak Tests

A test suite can execute every line of an important function and still fail to detect that the function is wrong. Coverage tells you which code ran. It does not tell you whether the assertions would notice a meaningful defect in that code. Mutation testing approaches the problem from the other direction. A mutation testing tool makes small, deliberate changes to production code and runs the tests. If the tests fail, they detected the change. If the tests still pass, the altered behavior has exposed a possible weakness in the suite.