What problem does it solve? Writing tests after implementation often produces brittle tests coupled to internal structure that break during refactors and fail to verify real behavior. This Skill enforces a disciplined red-green-refactor loop so every test verifies observable behavior through public interfaces. ## Core Features & Use Cases - Red-Green-Refactor Discipline: Enforces writing a failing test first, then the minimal implementation, then refactoring only while green. - Test Quality Standards: Defines what a good test is, where tests belong (seams at public interfaces), and anti-patterns to avoid such as tautological assertions and implementation-coupled mocks. - Mocking Guidance: Explains when to mock real system boundaries (external APIs, databases, time, file system) versus testing project logic directly, with dependency injection patterns in C++. - Use Case: When adding a new feature to a C++ module, use this Skill to drive the work one vertical slice at a time — one failing test, one minimal implementation, one refactor — producing tests that survive refactors. ## Quick Start Use the tdd skill to implement this feature test-first, starting with a failing test through the public interface.
