TDD (Red-Green-Refactor)
Use this skill whenever you need reliable, incremental implementation with test-first development.
When to use
- Building new behavior where correctness matters
- Fixing bugs with a reproducible failing test
- Refactoring safely with behavior locked by tests
- Working in codebases where regression risk is high
Workflow
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Red
- Write or update a test that describes the intended behavior.
- Run tests and verify the new/changed test fails for the right reason.
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Green
- Implement the smallest possible code change to make the failing test pass.
- Run the smallest relevant test scope first, then broader tests.
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Refactor
- Improve naming, remove duplication, simplify logic.
- Keep behavior unchanged and run tests again.
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Repeat
- Continue in small cycles until acceptance criteria are complete.
Guardrails
- Never skip the failing test step.
- Keep each cycle small and reviewable.
- Prefer deterministic tests over timing/network fragile tests.
- If behavior is unclear, stop and ask for clarification before coding.
Deliverables
- Final passing tests for all new/changed behavior
- Minimal implementation changes
- Brief summary of what each red-green-refactor cycle achieved