tdd

name	tdd
description	Guide Test-Driven Development using Kent Beck's Red-Green-Refactor cycle. Use when writing tests, implementing features via TDD, or following plan.md test instructions.

TDD (Test-Driven Development)

Kent Beck's Red-Green-Refactor cycle with Tidy First principles. This file owns the rules that span the whole cycle; read each phase's detail file as you enter that phase, so the per-phase guidance is in front of you while you act on it.

Phase	Runs	Does	Detail
RED	once per cycle	Write ONE small failing test	$HOME/.claude/skills/tdd/references/red.md
GREEN	once per cycle	Make it pass with minimal code, then commit	$HOME/.claude/skills/tdd/references/green.md
REFACTOR	loops	Improve structure with no behavior change, commit each step	$HOME/.claude/skills/tdd/references/refactor.md

REFACTOR loops until the code is clean; then the next behavior starts a new cycle back at RED.

Cross-phase invariants

These hold across every phase — the phase files don't restate them:

• One test at a time. Each RED adds exactly one failing test; one behavior per test keeps every failure a single, unambiguous signal.
• Run ALL tests after every change. The suite, not just the test at hand, is what tells you a change was safe.
• Tidy First — separate structural from behavioral changes. Behavior is feat:/fix: (committed at GREEN); structure is refactor: (committed during REFACTOR). Never mix them in one commit: a reviewer must be able to trust a refactor: touched no behavior.
• Commit cadence. Never during RED (a red bar isn't safe); at GREEN — the checkpoint you can always return to; after each refactor step.
• Never skip REFACTOR. A cycle isn't done at the green bar; it's done after the cleanup — skipping it is how a passing test today becomes unmaintainable code tomorrow.