| name | tdd |
| description | Apply when the task requires implementing net-new behavior — features, modules, endpoints, integrations, or any additive change. Drives development through strict red-green-refactor with test-first slicing and deterministic verification.
|
TDD Skill
Strict red-green-refactor for all net-new behavior. Test-first, one behavior slice at a time.
Constraints
- Test-first — no production code without a failing test that demands it.
- Minimal diff — no unrelated refactors, renames, or formatting churn.
- Deterministic — control time, randomness, I/O, and concurrency via seams/fakes.
- Fail fast — no silent error swallowing without a test proving the intent.
Cycle
Per behavior slice, execute the canonical red-green-refactor loop:
- Red — one test, failing for the right reason. Name encodes behavior + condition.
- Green — minimum production code to pass. No speculative abstraction (Rule of Three).
- Refactor — remove duplication, tighten names, simplify flow. Behavior unchanged.
- Verify — run smallest relevant target first, then full suite. Report commands + outcomes.
Output
- Intent: one sentence.
- Test slices: 3-7 bullets, ordered.
- Changes: tests added/updated + production code, by file.
- Verification: commands + pass/fail.
- Risks: contract changes, flaky-test vectors, uncovered boundaries.
