What problem does it solve?
This Skill eliminates the risk of writing fragile, implementation-coupled tests that break during code refactors, and avoids the horizontal slicing anti-pattern where bulk test writing leads to validating imagined behavior instead of actual user-facing system functionality.
Core Features & Use Cases
- Vertical Slice TDD Workflow: Enforces one-test-one-implementation tracer bullet cycles instead of writing all tests before all code, ensuring tests validate real behavior as it is built.
- Behavior-Focused Test Guidelines: Provides clear rules for writing integration-style tests that verify public interfaces, survive internal refactors, and describe what the system does rather than how it does it.
- Supporting Best Practices: Includes reference materials for designing deep modules, creating testable interfaces, proper mocking at system boundaries only, and identifying refactor opportunities after TDD cycles.
- Use Case: For example, when building a new user authentication feature, use this Skill to first write a test for successful email/password login, implement the minimal code to pass the test, then refactor the internal auth logic without breaking the test.
Quick Start
Use the tdd skill to implement the new order export feature by first writing a test for exporting orders to CSV, then writing the minimal code to pass that test, followed by refactoring once all tests pass.
