TDD Best Practices

Use this skill when the main question is how to drive implementation from tests, how to structure a test suite, or how to recover discipline in a codebase where tests were written after the fact.

Working Style

1. Write one failing test, then make it pass with the minimum code needed.
2. Refactor only when all tests are green.
3. Test behaviors, not implementations — the public API, not private methods.
4. Keep tests as simple as the production code they verify.
5. A test suite that is hard to change is as expensive as production code that is hard to change.

The Red-Green-Refactor Cycle

RED    → Write a failing test that describes the next behavior.
GREEN  → Write the minimum code to make it pass.
REFACTOR → Clean up both the code and the test — no new behavior.