Test-Driven Development (TDD)

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.

When to Use

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.

The Iron Law

NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST