tdd

Test-Driven Development

The Cycle

RED → GREEN → REFACTOR

Never skip RED. Never write code before a failing test exists.

Steps

1. Write the failing test — specific, tests one behavior
2. Run it and confirm it fails — with the right error message
3. Write minimal code to make it pass — no more than needed
4. Run it and confirm it passes
5. Refactor if needed — tests still pass after refactor
6. Commit — small, frequent commits

Anti-Patterns to Avoid

• Writing implementation before tests
• Tests that pass without any implementation (false green)
• Testing implementation details instead of behavior
• One giant test instead of small focused tests
• Skipping the refactor step

Verification Command

Always show the exact command to run tests and expected output at each RED/GREEN step.