TDD Skill
Write the test first. Watch it fail. Write minimal code to pass.
The Iron Law
No production code without a failing test first.
Every line of production code must be justified by a test that failed without it. No exceptions. No shortcuts. No "I'll test after."
Agent Workflow
1. DETECT -> Identify stack, test framework, existing test patterns
2. RED -> Write ONE failing test for the next behavior
3. VERIFY -> Run test, confirm it fails for the EXPECTED reason
4. GREEN -> Write the SIMPLEST code that makes the test pass
5. VERIFY -> Run tests, confirm ALL pass (new + existing)
6. REFACTOR -> Clean up while keeping all tests green
7. REPEAT -> Next behavior = next failing test
CRITICAL: Never skip VERIFY steps. A test that passes on first run proves nothing.
RED-GREEN-REFACTOR Cycle
See references/red-green-refactor.md for the detailed cycle with rules and verification steps.
Reference Guide
| Topic | Reference | |-------|-----------| | Full RED-GREEN-REFACTOR cycle | red-green-refactor.md | | Common mistakes and red flags | anti-patterns.md | | Per-stack test commands | stack-commands.md |
Quick Reference: Test Commands
| Stack | Run Tests | Watch Mode |
|-------|-----------|------------|
| React/Next.js | npx vitest run | npx vitest |
| Laravel | php artisan test | php artisan test --watch |
| Swift | swift test | - |
| Generic TS | bunx vitest run | bunx vitest |
| Go | go test ./... | - |
| Rust | cargo test | cargo watch -x test |
Forbidden Behaviors
- Never write production code before a failing test
- Never skip the VERIFY RED step
- Never accept a test that passes on first run without investigation
- Never mock what you can test directly
- Never write more than one test at a time in RED phase
- Never add features beyond what the current test requires