Test-Driven Development Write one failing test that describes the next behavior, write the minimal code to pass it, then refactor while green. Every production change starts with a test that proves the need exists. This is the discipline within each vertical slice — not framework syntax, but when and why to write tests. Skip for exploratory prototyping, config-only changes (environment variables, feature flags), visual/CSS-only tweaks, and one-off scripts that won't be maintained. Quick Reference — TDD Cycle | Phase | Action | Rule | | -------- | ----------------------------------------------…