Test-Driven Development (TDD) Overview Write the test first. Watch it fail. Write minimal code to pass. Core principle: If you didn't watch the test fail, you don't know if it tests the right thing. Violating the letter of the rules is violating the spirit of the rules. When to Use Use for behavior changes where a repeatable test can demonstrate the requirement or reproduce the bug. Inspect the repository’s test runner and existing coverage first. For copy, generated outputs or low-impact configuration, use the appropriate focused validation rather than manufacturing a unit test. Preserve exi…