test-driven-development

Topics in the source

• Test-Driven Development (TDD)
• Overview
• When to Use
• The Iron Law
• Red-Green-Refactor
• RED - Write Failing Test
• Verify RED - Watch It Fail
• GREEN - Minimal Code

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. 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. 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. Write one minimal test showing what should happen. Clear name, tests real behavior, one thing Vague name, tests mock not code Requirements: One behavior Clear name Real code (no mocks unless unavoidable) MANDATORY. Never skip. Confirm: Test fails (not errors) Failure message is expected Fails because feature missing (not typos) Test passes? You're testing existing behavior. Fix test. Test errors? Fix error, re-run until it fails correctly. Write simplest code to pass the test. Just enough to pass Over-engineered Don't add features, refact

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