Mutation Testing - CI/CD Glossary Definition

Mutation testing evaluates test quality by seeding bugs and measuring how many the tests catch.

Mutation testing deliberately introduces small faults (mutants) into the code, then checks whether the test suite fails. Surviving mutants reveal weak or missing assertions.

Unlike coverage, which only shows what ran, mutation testing shows whether the tests actually verify behavior. Tools include Stryker, PIT, and mutmut.

In CI

Mutation testing is expensive because it reruns tests per mutant, so teams often run it on changed files or on a schedule rather than every push.

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