What problem does it solve? Code coverage proves lines were executed but not that assertions would catch real bugs. This Skill runs mutation testing to detect weak assertions by introducing controlled code changes (mutants) and checking whether the test suite kills them. ## Core Features & Use Cases - Per-language tool guidance: Canonical install and run commands for Stryker (JS/TS/.NET/Scala), PIT (JVM), Infection (PHP), mutmut and cosmic-ray (Python), go-mutesting and gremlins (Go), cargo-mutants (Rust), mutant (Ruby), and muter (Swift). - Surviving-mutant diagnosis: Catalogs common survivor patterns (off-by-one loops, boolean short-circuits, string-literal leaks, void side effects) with the exact assertion fix for each. - Mutation operator reference: Maps operator families (conditional boundary, arithmetic, logical, statement removal) to the test patterns that kill them. - Use Case: A Rust project's tests pass with 95% coverage, but cargo mutants reveals survivors in boundary comparisons; the Skill directs adding exact boundary-value tests (n, n-1, n+1) until the score threshold passes. ## Quick Start Run mutation testing on my project with the appropriate tool for its language and report any surviving mutants with fixes.
