tdd

What problem does it solve? Writing tests after implementation often produces brittle, implementation-coupled tests that break during refactors and fail to verify real behavior. This Skill enforces a disciplined test-first workflow so tests act as durable specifications of behavior. ## 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-Based Test Placement: Defines tests only at pre-agreed public interface boundaries, confirmed with the user before any test is written. - Anti-Pattern Detection: Identifies implementation-coupled, tautological, and horizontally sliced tests, with reference guides on good test design and mocking at system boundaries. - Use Case: When adding a checkout feature, confirm the public seams first, then write one failing test like "user can checkout with valid cart", implement just enough code to pass, and repeat for the next slice. ## Quick Start Ask the assistant to build the next feature using test-driven development, starting by agreeing on the seams to test and writing the first failing test.