| name | add-tdd |
| description | RED-GREEN-REFACTOR execution discipline for AI agents. Use when implementing any feature or bugfix that has (or should have) tests — forces a failing test confirmed for the right reason before any production code. Loaded by add.build and add.test. |
TDD — RED-GREEN-REFACTOR Discipline
LANG: Respond in user's native language. Tech terms in English.
Iron Law
NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST.
If you wrote implementation before its test: delete it, start over from RED. "Keep it as reference" is testing-after — delete means delete.
The Cycle (one feature at a time)
RED — write ONE failing test
- Write a test describing the expected behavior (from the acceptance criterion / contract).
- Run the test. It MUST fail.
- Confirm it fails for the RIGHT reason: missing implementation, wrong return value, unmet condition — NOT a syntax error, import error, or typo.
- If it passes: the feature already exists or the test is wrong. Investigate before continuing.
GREEN — minimal code to pass
- Write the smallest code that makes the test pass. No cleverness, no optimization, no extra features.
- Run the test. It MUST pass.
- Run the existing suite. No regressions.
REFACTOR — only while GREEN
- Improve names, remove duplication, extract helpers.
- Tests stay green. Never refactor while RED — get to GREEN first.
- Do not add behavior during refactor.
Then loop to RED for the next behavior. One test ↔ one implementation step. Do not write all tests first then all implementation (horizontal slicing produces tests for imagined, not actual, behavior).
Anti-Rationalization
| Rationalization | Reality |
|---|
| "I'll add the test right after" | You won't, and the code will shape the test. Test first, always. |
| "I need to see the design first" | The test IS the design. Let it drive the interface. |
| "Already wrote it, deleting is wasteful" | Sunk cost. Delete it. Start from RED. |
| "The test passes immediately, good" | It proves nothing — it never failed. Fix the test or pick new behavior. |
| "Syntax error counts as RED" | No. It must fail because the behavior is missing. |
| "I'll batch these trivial features" | Trivial enough to batch = trivial enough to skip TDD; use a plain task. |
When NOT to use
- Throwaway spikes / exploratory prototypes you will delete.
- Pure config or doc changes with no behavior.
- Generated code with no logic.
Bug-fix mode
When a bug is reported: do not start by fixing it. First write a test that reproduces it (RED), then fix to GREEN.
