Mutation Testing

<default_to_action> When validating test quality or improving test effectiveness:

1. MUTATE code (change + to -, >= to >, remove statements)
2. RUN tests against each mutant
3. VERIFY tests catch mutations (kill mutants)
4. IDENTIFY surviving mutants (tests need improvement)
5. STRENGTHEN tests to kill surviving mutants

Quick Mutation Metrics:

• Mutation Score = Killed / (Killed + Survived)
• Target: > 80% mutation score
• Surviving mutants = weak tests

Critical Success Factors:

• High coverage ≠ good tests (100% coverage, 0% assertions)
• Mutation testing proves tests actually catch bugs
• Focus on critical code paths first