TDD Skill
SKILL.md
Test-Driven Development (TDD)
Overview
Write the test first. Watch it fail. Write minimal code to pass.
Core principle: If you didn't watch the test fail, you don't know if it tests the right thing.
Violating the letter of the rules is violating the spirit of the rules.
When to Use
Always:
- New features
- Bug fixes
- Refactoring
- Behavior changes
Exceptions (ask your human partner):
- Throwaway prototypes
- Generated code
- Configuration files
Thinking "skip TDD just this once"? Stop. That's rationalization.
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.
Red-Green-Refactor
- RED: Write one minimal failing test. Verify it fails correctly (not error, but assertion failure).
- GREEN: Write minimal code to pass the test. No more.
- REFACTOR: Clean up code and tests. Verify tests still pass.
- REPEAT
Verification Checklist
Before marking work complete:
- Every new function/method has a test
- Watched each test fail before implementing
- Each test failed for expected reason (feature missing, not typo)
- Wrote minimal code to pass each test
- All tests pass
- Output pristine (no errors, warnings)