develop-tddlisted

# Develop TDD > **HARD GATE** — Do NOT proceed if on `main` or `master`. Run `kickoff-branch` first to create a feature branch or worktree. > > **HARD GATE** — Do NOT write code before you have a plan. New feature: `plan-work` → epic capsule tasks. Bug: `investigate-bug` → `specs/bugs/BUG-*.md` (or use `fix-bug` orchestrator). > > **RECURSIVE DISCIPLINE** — This lifecycle apply to EVERY task, including updating these skills. Never skip planning because a task is "meta" or "just documentation." ## Philosophy **Core principle**: Tests should verify behavior through public interfaces, not implementation details. Code can change entirely; tests shouldn't. **Good tests** are integration-style: they exercise real code paths through public APIs. They describe _what_ the system does, not _how_ it does it. A good test reads like a specification — "user can checkout with valid cart" tells you exactly what capability exists. These tests survive refactors because they don't care about internal structure. **Bad tests** are coupled to implementation. They mock internal collaborators, test private methods, or verify through external means. The warning sign: your test breaks when you refactor, but behavior hasn't changed. See [tests.md](tests.md) for examples and [mocking.md](mocking.md) for mocking guidelines. ## Anti-Pattern: Horizontal Slices **DO NOT write all tests first, then all implementation.** This is "horizontal slicing" — treating RED as "write all tests" and GREEN as "wr