Test-Driven Development (TDD)

Priority: P1 (OPERATIONAL)

The Iron Law

NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST. If you wrote code before the test: Delete it. Start over. No "adapting" or keeping as reference.

The TDD Cycle

1. RED: Write a minimal failing test. Verify failure (Expected error, not typo).
2. GREEN: Write the simplest code to pass. Verify pass (Pristine output).
3. REFACTOR: Clean up code while staying green.

Core Principles

• Watch it Fail: If you didn't see it fail, you didn't prove the test works.
• Minimalism: Don't add features/options beyond the current test (YAGNI).
• Real Over Mock: Prefer real dependencies unless they are slow/flaky. Avoid Anti-Patterns.

Verification Checklist

• Every new function/method has a failing test first?
• Failure message was expected (feature missing, not setup error)?
• Minimal code implemented (no over-engineering)?
• Common Pitfalls avoided?

Expert References

• TDD Patterns & Discovery Protocols
• Testing Anti-Patterns (Safety First)