Test-Driven Development (TDD)

Core Principle

Write tests before code. Always. TDD is not about testing—it's about design through small, disciplined steps.

When to Use This Skill

• User explicitly requests TDD ("use TDD", "test first", "test-driven")
• Implementing new features
• Fixing bugs (write failing test that reproduces bug first)
• Refactoring existing code (ensure tests exist first)

The Three Laws (Never Violate)

1. Write NO production code without a failing test first
2. Write only enough test to demonstrate one failure
3. Write only enough code to pass that test