run-mutation-tests

name	run-mutation-tests
description	Use this skill when running mutation tests or interpreting mutation test results. Covers running Pitest, interpreting surviving mutants, and documenting unkillable mutations.

Run Mutation Tests

Use this skill after tests pass, to verify mutation test coverage.

Read .github/instructions/testing.instructions.md for the mutation testing conventions. Then:

1. Run mutation tests: ./run-branch-mutation-tests.sh.
2. Find surviving mutants in <module>/target/pit-reports/mutations.csv. Focus on SURVIVED and NO_COVERAGE entries.
3. For each surviving mutant, either:
   • Add a test that detects the mutation.
   • Simplify the production code if the mutated path is unreachable.
   • Document with // XXX: if genuinely unkillable (see testing conventions).
4. Re-run to verify that all killable mutants are killed.
5. Commit any changes.