tddlisted

# Test-Driven Development ## The Iron Law ``` NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST ``` Write code before the test? Delete it. Start over. **No exceptions:** - Don't keep it as "reference" - Don't "adapt" it while writing tests - Don't look at it - Delete means delete Implement fresh from tests. Period. ## Protecting the Tests The agent optimizes for green. These rules make green mean true. Every one of them closes a loophole that was actually exploited in real projects using this skill (a July 2026 audit found 18 of 25 E2E tests in one repo permanently `test.skip`-guarded — they had never run once — and Anthropic, METR, and Kent Beck all document agents disabling or deleting tests to pass). ``` 1. EVIDENCE THE RED Run the new test and SHOW its failing output before writing any implementation. It must fail for the right reason — the missing behavior, not an import error or typo. No observed red = the cycle never happened. 2. FIX CODE, NOT TESTS Never delete, weaken, .skip, or loosen a test to reach green. If you believe the test itself is wrong, STOP, say so explicitly, and get the user's agreement before changing it. 3. SKIPPED = FAILING "7 passed, 18 skipped" is a red suite. Always report full counts (passed / failed / skipped).