Mutation Score - CI/CD Glossary Definition
Mutation score is the ratio of killed mutants to total mutants, a measure of test suite strength.
Mutation score is the percentage of introduced mutants that the test suite detected (killed) out of all viable mutants. A higher score means the tests are more effective at catching regressions.
Mutants that survive (are not caught) point to code paths the tests execute but do not truly verify. Equivalent mutants, which cannot change observable behavior, are excluded from the calculation where possible.
Reading the number
A project with 90% line coverage but a 40% mutation score has tests that run the code without asserting much about it.
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