tdd

What problem does it solve? Writing tests after code often produces brittle, implementation-coupled tests that break on every refactor. This Skill enforces a disciplined test-first workflow so tests verify real behavior through public interfaces and survive internal changes. ## Core Features & Use Cases - Red-Green Loop Discipline: Enforces writing a failing test before any implementation, one vertical slice at a time, with no speculative features. - Seam Identification: Helps you define and confirm the public boundaries (seams) where tests belong before writing any test code. - Anti-Pattern Detection: Flags implementation-coupled, tautological, and horizontally-sliced tests with concrete good/bad examples. - Mocking Guidelines: Provides rules for mocking only at system boundaries (external APIs, time, file system) and designing mockable interfaces via dependency injection. - Use Case: When adding a checkout feature, use this Skill to agree on the seams with the user, write one failing behavior test, implement the minimal code to pass it, and repeat until the feature is complete. ## Quick Start Ask the AI to build the next feature using test-driven development, starting by agreeing on the seams to test and writing one failing test first.