tdd

What problem does it solve? Writing tests after implementation often produces tests coupled to internal structure that break during refactors, while writing all tests upfront produces tests of imagined behavior. This Skill enforces a disciplined red-green-refactor workflow that keeps tests focused on observable behavior through public interfaces. ## Core Features & Use Cases - Red-Green-Refactor Loop: Drives one test and one minimal implementation at a time using vertical tracer-bullet slices instead of horizontal batching. - Behavior-Focused Test Design: Provides guidelines and examples for writing integration-style tests that survive refactors, plus rules for when mocking at system boundaries is appropriate. - Interface Design Guidance: Includes references on deep modules, dependency injection, and testability-oriented interface design. - Use Case: When asked to build a new feature like a checkout flow, the Skill plans the public interface with the user, writes one failing test, implements the minimal code to pass, and repeats until all prioritized behaviors are covered. ## Quick Start Ask the assistant to build a feature or fix a bug using test-driven development with the red-green-refactor loop.