TDD

Overview

Write the test first. Watch it fail. Write the minimal code to pass. Refactor.

Core principle: if you didn't watch the test fail, you don't know it tests the right thing.

REQUIRED COMPANION: use test-design for what to feed, assert, and mock. This skill is only the rhythm. Formalistic RED tests are still forbidden — a failing theater test proves nothing.

When to Use

Always: new features, bug fixes, refactoring, behavior changes.

Exceptions (ask the human first): throwaway prototypes, generated code, pure config with no behavior.

Thinking "skip TDD just this once"? Stop — that's rationalization.

The Iron Law (non-negotiable)