Mutation testing evaluerer kvaliteten af en testsuite ved bevidst at introducere små bugs ("mutanter") i koden og kontrollere, om testene opdager dem. Det måler, hvor gode tests faktisk er til at detektere fejl — langt ud over coverage, som kun måler udførelse.
Hvordan mutation testing fungerer
1. A tool makes small changes (MUTATIONS) to the code, e.g.:
→ change + to -, > to >=, true to false, remove a statement, change a constant
→ each mutation = a deliberate "bug" (a MUTANT version of the code)
2. Run the TEST SUITE against each mutant:
→ tests FAIL → the mutant is "KILLED" (good — tests caught the bug) ✓
→ tests PASS → the mutant "SURVIVED" (bad — tests DIDN'T catch the bug) ✗
3. MUTATION SCORE = % of mutants killed → measures how good the tests are at catching bugs
