Write the test first, then write the smallest change that makes it pass, then refactor safely.
Core loop
- Red: write a failing test that expresses the desired behavior.
- Green: implement the minimum change to pass.
- Refactor: improve structure while keeping tests green.
Quick Start
- Start from the public interface (API, function, UI behavior), not private helpers.
- Prefer “behavioral” test names (what), not “implementation” names (how).
- When fixing bugs: reproduce with a test first.
Guardrails
- Don’t over-mock: prefer integration at boundaries; mock only slow/flaky externals.
- Keep tests deterministic: control time, randomness, and network.
- If a test is hard to write, your design likely needs an interface seam.
Red/Green/Refactor checklist
- Red: test fails for the right reason (not setup errors).
- Green: smallest change to pass, no extra behavior.
- Refactor: improve structure without changing behavior or tests.
References
- Common anti-patterns:
references/testing-anti-patterns.md