TDD Skill

Write the test first. Watch it fail. Write minimal code to pass.

The Iron Law

No production code without a failing test first.

Every line of production code must be justified by a test that failed without it. No exceptions. No shortcuts. No "I'll test after."

Agent Workflow

code

1. DETECT  -> Identify stack, test framework, existing test patterns
2. RED     -> Write ONE failing test for the next behavior
3. VERIFY  -> Run test, confirm it fails for the EXPECTED reason
4. GREEN   -> Write the SIMPLEST code that makes the test pass
5. VERIFY  -> Run tests, confirm ALL pass (new + existing)
6. REFACTOR -> Clean up while keeping all tests green
7. REPEAT  -> Next behavior = next failing test

CRITICAL: Never skip VERIFY steps. A test that passes on first run proves nothing.

RED-GREEN-REFACTOR Cycle

See references/red-green-refactor.md for the detailed cycle with rules and verification steps.

Reference Guide

Topic	Reference
Full RED-GREEN-REFACTOR cycle	red-green-refactor.md
Common mistakes and red flags	anti-patterns.md
Per-stack test commands	stack-commands.md

Quick Reference: Test Commands

Stack	Run Tests	Watch Mode
React/Next.js	`npx vitest run`	`npx vitest`
Laravel	`php artisan test`	`php artisan test --watch`
Swift	`swift test`	-
Generic TS	`bunx vitest run`	`bunx vitest`
Go	`go test ./...`	-
Rust	`cargo test`	`cargo watch -x test`

Forbidden Behaviors

•Never write production code before a failing test
•Never skip the VERIFY RED step
•Never accept a test that passes on first run without investigation
•Never mock what you can test directly
•Never write more than one test at a time in RED phase
•Never add features beyond what the current test requires