add-tddlisted

# 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 1. Write a test describing the expected behavior (from the acceptance criterion / contract). 2. Run the test. It **MUST fail**. 3. Confirm it fails for the **RIGHT reason**: missing implementation, wrong return value, unmet condition — **NOT** a syntax error, import error, or typo. 4. If it passes: the feature already exists or the test is wrong. Investigate before continuing. ### GREEN — minimal code to pass 1. Write the **smallest** code that makes the test pass. No cleverness, no optimization, no extra features. 2. Run the test. It **MUST pass**. 3. Run the existing suite. No regressions. ### REFACTOR — only while GREEN 1. Improve names, remove duplication, extract helpers. 2. Tests stay green. **Never refactor while RED** — get to GREEN first. 3. 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