tdd

What problem does it solve? Writing tests after implementation often produces brittle tests coupled to internal structure that break during refactors. This Skill enforces a disciplined test-first workflow where tests verify observable behavior through public interfaces, so they survive internal changes. ## Core Features & Use Cases - Red-Green-Refactor Workflow: Walks through planning, a tracer-bullet first test, an incremental one-test-at-a-time loop, and a final refactor pass. - Test Quality Guidance: Distinguishes behavior-focused integration tests from implementation-coupled tests, with rules for when and how to mock at system boundaries. - Interface Design Support: Provides principles for deep modules and testable interfaces using dependency injection and small surface areas. - Use Case: When building a new checkout feature, use this Skill to write one failing test for the first behavior, implement minimal code to pass it, then repeat per behavior before refactoring. ## Quick Start Use the tdd skill to build the new feature test-first, one behavior at a time through the red-green-refactor loop.