What problem does it solve? Writing meaningful tests for plain TypeScript/JavaScript code is hard: teams pick the wrong runner, over-mock modules until broken wiring ships green, misuse fake timers and env stubs, and inflate coverage with assertion-free specs. This Skill provides the conventions for writing tests worth counting and auditing suites that only look trustworthy. ## Core Features & Use Cases - Runner routing and test strategy: Detects the workspace's existing runner (Vitest by default, Jest where signaled, node:test as the zero-dependency floor) and applies role-based strategies for pure modules, boundary seams, DOM-adjacent code, Node-runtime code, and published type surfaces. - Mock-masking prevention: Requires one smoke spec that imports the real public entry and builds the object graph unmocked, so broken export maps or mis-wired factories fail a spec instead of the consumer. - Suite audit and mutation testing: The bundled references/suite-audit.md catalogs false-confidence anti-patterns (no assertions, tautological checks, missing awaits, swallowed exceptions), a red-check verification method, and StrykerJS mutation testing guidance. - Use Case: When asked to review an existing Vitest suite that reports 90% coverage, load this Skill to scan for coverage-touching sweeps and unawaited async assertions, prove each finding by temporarily breaking the guarded behavior, then run StrykerJS on critical modules to expose surviving mutants. ## Quick Start Review my TypeScript test suite for weak assertions and over-mocking, and tell me which specs would survive a mutation testing run.
