tdd

What problem does it solve? Writing tests after implementation often produces brittle tests coupled to internal structure, while writing all tests upfront produces tests of imagined behavior. This Skill enforces a disciplined test-driven development workflow that keeps tests focused on observable behavior through public interfaces. ## Core Features & Use Cases - Red-Green-Refactor Loop: Implements one test and one minimal implementation per cycle using vertical tracer-bullet slices instead of horizontal batching. - Behavior-Focused Testing Guidance: Distinguishes good integration-style tests from implementation-coupled tests, with rules for when and how to mock at system boundaries. - Design References: Includes guidance on deep modules, interface design for testability, and post-cycle refactoring candidates. - Use Case: When adding a checkout feature, confirm the public interface and priority behaviors with the user, write one failing test, implement the minimal code to pass, and repeat until all behaviors are covered before refactoring. ## Quick Start Use the tdd skill to build the new shopping cart feature with a red-green-refactor workflow, one behavior at a time.