# Test Driven Development

> Use when implementing any feature or bugfix, before writing implementation code

Use when implementing any feature or bugfix, before writing implementation code

- Page: https://ss33.ai/skills/dokhacgiakhoa/test-driven-development-18746142540
- Publisher: dokhacgiakhoa
- Category: [Software Development](https://ss33.ai/skills/category/software-development-t44z8z) › [Testing & QA](https://ss33.ai/skills/category/software-development-t44z8z/testing-and-qa-g56s6z)
- License: MIT
- Source: https://github.com/dokhacgiakhoa/agent-skills-4-vibe-coding-cli/blob/c4a059bbf7a8d6b2162071f0fbfe74053faa6d20/.agent/skills/test-driven-development/SKILL.md

## Skill

SKILL.md: https://ss33.ai/api/v1/ss33/download/dokhacgiakhoa/test-driven-development-18746142540

# Test-Driven Development (TDD)

## Overview

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

**Core principle:** If you didn't watch the test fail, you don't know if it tests the right thing.

**Violating the letter of the rules is violating the spirit of the rules.**

## When to Use

**Always:**
- New features
- Bug fixes
- Refactoring
- Behavior changes

**Exceptions (ask your human partner):**
- Throwaway prototypes
- Generated code
- Configuration files

Thinking "skip TDD just this once"? Stop. That's rationalization.

## The Iron Law

```
NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST
```

Write code before the test? Delete it. Start over.

**No exceptions:**
- Don't keep it as "reference"
- Don't "adapt" it while writing tests
- Don't look at it
- Delete means delete

Implement fresh from tests. Period.

## Red-Green-Refactor

```dot
digraph tdd_cycle {
    rankdir=LR;
    red [label="RED\nWrite failing test", shape=box, style=filled, fillcolor="#ffcccc"];
    verify_red [label="Verify fails\ncorrectly", shape=diamond];
    green [label="GREEN\nMinimal code", shape=box, style=filled, fillcolor="#ccffcc"];
    verify_green [label="Verify passes\nAll green", shape=diamond];
    refactor [label="REFACTOR\nClean up", shape=box, style=filled, fillcolor="#ccccff"];
    next [label="Next", shape=ellipse];

    red -> verify_red;
    verify_red -> green [label="yes"];
    verify_red -> red [label="wrong\nfailure"];
    green -> verify_green;
    verify_green -> refactor [label="yes"];
    verify_green -> green [label="no"];
    refactor -> verify_green [label="stay\ngreen"];
    verify_green -> next;
    next -> red;
}
```

## 🧠 Knowledge Modules (Fractal Skills)

### 1. [RED - Write Failing Test](./sub-skills/red-write-failing-test.md)
### 2. [Verify RED - Watch It Fail](./sub-skills/verify-red-watch-it-fail.md)
### 3. [GREEN - Minimal Code](./sub-skills/green-minimal-code.md)
### 4. [Verify GREEN - Watch It Pass](./sub-skills/verify-green-watch-it-pass.md)
### 5. [REFACTOR - Clean Up](./sub-skills/refactor-clean-up.md)
### 6. [Repeat](./sub-skills/repeat.md)