Mutation testing is a software testing technique designed to evaluate the quality of your test suite by introducing small, controlled changes (mutations) to the code and then checking whether the existing tests can detect these changes. The idea is that if your test suite is robust, it should fail when the code is altered in ways that introduce defects or bugs.
How Mutation Testing Works:
- Create Mutants:
- Mutants are versions of the original code with small modifications, such as:
- Changing arithmetic operators (e.g.,
+to-). - Modifying conditional expressions (e.g.,
>to<). - Altering logical operators (e.g.,
&&to||). - These mutations simulate common coding errors that developers might make.
- Run Test Suite Against Mutants:
- The test suite is executed against each mutant.
- If a test case fails when executed against a mutant, the mutant is considered “killed,” meaning the test suite detected the introduced fault.
- If all tests pass, the mutant “survives,” indicating that the test suite may be insufficient in detecting that particular type of fault.
- Analyze Results:
- The effectiveness of the test suite is measured by the mutation score, which is the ratio of killed mutants to the total number of mutants generated.
- A high mutation score (close to 100%) suggests that the test suite is effective at catching errors.
- Surviving mutants may indicate gaps in the test suite, prompting the need to write additional test cases.