tdd

What problem does it solve? Writing tests after code often produces brittle, implementation-coupled tests that break on refactors and fail to verify real behavior. This Skill enforces a disciplined red-green loop so every test verifies observable behavior through public interfaces. ## Core Features & Use Cases - Seam-Based Test Design: Identifies public interface boundaries before writing tests, ensuring tests survive refactors and target critical paths. - Anti-Pattern Detection: Flags implementation-coupled, tautological, and horizontally-sliced tests that pass by construction or break without behavior changes. - Mocking Guidelines: Defines when to mock (system boundaries only) and how to design mockable interfaces via dependency injection and SDK-style APIs. - Use Case: When adding a checkout feature, use this Skill to write one failing test at the checkout seam, implement the minimal code to pass it, then repeat in vertical slices instead of writing all tests upfront. ## Quick Start Ask the assistant to build the next feature using test-driven development with one failing test at a confirmed public seam before any implementation.