tdd

npx skills add sickn33/agentic-awesome-skills --skill tdd --agent claude-code

Same command for any agent — swap --agent for codex, cursor, copilot.

# Test-Driven Development ## When to Use Use when this workflow matches the user request: Use this skill for its documented workflow. _Source: [mattpocock/skills](https://github.com/mattpocock/skills) (MIT)._ ## Philosophy **Core principle**: Tests should verify behavior through public interfaces, not implementation details. Code can change entirely; tests shouldn't. **Good tests** are integration-style: they exercise real code paths through public APIs. They describe _what_ the system does, not _how_ it does it. A good test reads like a specification - "user can checkout with valid cart" tells you exactly what capability exists. These tests survive refactors because they don't care about internal structure. **Bad tests** are coupled to implementation. They mock internal collaborators, test private methods, or verify through external means (like querying a database directly instead of using the interface). The warning sign: your test breaks when you refactor, but behavior hasn't changed. If you rename an internal function and tests fail, those tests were testing implementation, not behavior. See [tests.md](tests.md) for examples and [mocking.md](mocking.md) for mocking guidelines.