# Tdd

> Test-driven development — write tests first, implement second, refactor third

- Skill: `lucassantana-dev/tdd` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add lucassantana-dev/tdd`
- Raw SKILL.md: https://api.skillmd.com/api/skills/lucassantana-dev/tdd/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: LucasSantana-Dev (https://skillmd.com/u/lucassantana-dev)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/lucassantana-dev/tdd

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# TDD

Write the test before the implementation. Always.

## Cycle

```text
RED    → Write a failing test that captures expected behavior
GREEN  → Write the minimum code to make it pass
REFACTOR → Clean up while tests stay green
```

## Steps

1. Understand the requirement
2. Write one failing test for the happy path
3. Run it — confirm it fails for the right reason
4. Write minimum implementation to pass
5. Run it — confirm green
6. Refactor if needed (tests must stay green)
7. Add edge case tests after happy path works

## Rules

- Never write implementation before the test exists
- Test behavior, not implementation details
- One assertion focus per test
- If you cannot write a test, clarify the requirement first
- Mock external dependencies; do not mock internal logic
- Coverage is a signal, not a target — test business value