Tdd

This is a principled TDD workflow that fights the two most common mistakes: writing tests that break when you refactor, and writing all your tests before any implementation. It pushes you to test behavior through public interfaces, not implementation details, so your tests survive internal changes. The workflow is vertical slicing, one test and implementation at a time, with planning up front to agree on what actually matters. You get a tracer bullet first to prove the path works end to end, then iterate. The philosophy is opinionated but right: good tests read like specs and don't care how you built it, bad tests mock internals and shatter during refactors. Includes concrete checklists and anti-patterns.