What problem does it solve? Writing tests after the fact produces suites that mirror implementation details, miss edge cases, and break on harmless refactors. This Skill enforces test-first development so every behaviour is specified by a failing test before any production code exists, and keeps existing suites fast, deterministic, and trustworthy. ## Core Features & Use Cases - Red-Green-Refactor Cycle: Writes one failing test per behaviour, the minimum code to pass it, then refactors with the suite green, with each step shown separately. - Scope Selection: Chooses between unit, integration, contract, and end-to-end tests based on what must fail when the behaviour breaks, including component-library-specific scopes like boundary and mutation tests. - Suite Auditing: Detects assertion-free tests, shared mutable state, ordering dependencies, over-mocking, and coverage that measures lines instead of behaviour, with tiered findings and fixes. - Legacy Recovery: Pins current behaviour with characterisation tests before changing untested code, then resumes the normal cycle from a green baseline. - Use Case: When adding a feature to a React component library, use this Skill to plan the ordered list of behaviours, drive each one with a failing Vitest test, and audit the resulting suite for flaky or brittle tests. ## Quick Start Use test-driven development to add a new behaviour to my component, starting with a failing test that specifies the expected outcome.
