Give every critical path a test that dies under a behavior-changing mutation. Map the untested critical surface (coverage × call-graph of the money/auth/data paths), write characterization tests that assert real behavior, prove each earns its keep by failing at its assertion under a mutation (harness still runnable — a compile break is not proof), and route surfaced bugs to a fix or backlog, looping until every confirmed critical path is mutation-audited. Use when "close the test gap", "cover the critical paths", "pin a characterization net", "test debt", "add tests before we refactor", characterization/mutation testing, missing coverage. Not for broken tests, nor flake e…
