mutation-test

Mutation testing measures test effectiveness by introducing small code changes (mutants) and checking if your tests catch them. A higher mutation score indicates stronger tests that detect actual bugs, not just line execution.

Yes. Mutation testing supports multi-language projects using language-specific tools: Stryker for JavaScript, mutmut for Python, and PITest for Java. Each generates a mutation report with scores and survivor analysis.

Mutation score is the percentage of introduced code mutations your tests detected and killed. Survivors are mutants your tests missed, revealing gaps in coverage and guiding which tests need improvement before release.

Configure the appropriate tool for your language (Stryker, mutmut, or PITest), run the mutation analysis on your test suite, then review the generated report for killed mutants, survivors, timeouts, and recommended test improvements.

Timeouts occur when introduced mutations cause infinite loops or extremely slow execution. The mutation report flags these alongside killed and survived mutants to give you a complete picture of test effectiveness and code behavior under mutation.