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