# Tdd

> 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. Use when this capability is needed.

- Skill: `tomevault-io/tdd-9` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/tdd-9`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/tdd-9/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/tdd-9

---


# TDD (Test-Driven Development)

Kent Beck's Red-Green-Refactor cycle with Tidy First principles.

## Workflow

```
/tdd:red -> write failing test -> /tdd:green -> pass test -> /commit
                                                                  |
      <- next feature <- /tdd:red <- satisfied? <- /tdd:refactor (repeat)
```

## Phases

| Phase | Command | Action |
|-------|---------|--------|
| RED | `/tdd:red` | Write ONE small failing test |
| GREEN | `/tdd:green` | Make it pass with minimal code, commit |
| REFACTOR | `/tdd:refactor` | Improve structure (no behavior change), commit each step |

## Core Principles

- **One test at a time**: Each RED adds exactly ONE failing test
- **Minimal code**: GREEN writes just enough to pass
- **Never skip REFACTOR**: Complete all three phases
- **Tidy First**: Separate structural changes (refactor) from behavioral changes (feat/fix)
- **Small commits**: Commit after GREEN, commit after EACH refactor

## GREEN Phase Strategies

| Confidence | Strategy | Use When |
|------------|----------|----------|
| Low | **Fake It** | Return constant, generalize later |
| High | **Obvious Implementation** | Solution is clear |
| Generalizing | **Triangulation** | Add test to break a fake |

## Quality Standards

- Eliminate duplication between test and production code
- Express intent through clear naming
- Keep methods small and focused
- Run ALL tests after EVERY change

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<!-- tomevault:4.0:skill_md:2026-04-13 -->