Mutation Minded Testing

Rewrite a weak unit spec into one that kills mutations. Use when you must fix a toBeTruthy/toBeDefined/toBeFalsy assertion, a bare mock-fired check, an array-length-only check, a shapeless snapshot, or a private-state peek. Triggers on "rewrite this spec", "stronger assertions", "catch mutations".

Grade and review an existing spec suite for kill power before adding more. Use when you must find whether specs are real or cosmetic — each gets STRONG/ACCEPTABLE/WEAK/KILL plus one mutation it survives. Triggers on "audit these tests", "how strong is this", "mutation score", "green but buggy".

Diagnose why a module is hard to verify and fix the narrowest seam. Use when specs need heavy mocking, break on refactor, or survive plausible mutations — find missing DI seams, hidden state, temporal coupling, raw clocks. Triggers on "tests are brittle", "mocks everywhere", "too coupled".

Close branch gaps with high-signal specs, not cosmetics. Use when you run a file to 100% branches or kill survivors from Stryker/Infection/Pitest/Mutmut. Lists semantic branches and writes one real check per outcome. Triggers on "uncovered branches", "cover this file", "mutation run".