fusengine/tdd

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

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
   IF the test fails for a DIFFERENT reason (syntax error, wrong import, missing fixture) → fix the test itself and re-run. Do NOT proceed to GREEN until the failure matches the intended behavior.
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