# Tdd

> Test-Driven Development (TDD) skill for Red-Green-Refactor cycle. Use when implementing features with tests first, minimal code to pass, then refactor. Teammates execute TDD autonomously within their own context in Agent Teams. Use when this capability is needed.

- Skill: `tomevault-io/tdd-16` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/tdd-16`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/tdd-16/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/tdd-16

---


# SKILL: Test-Driven Development (TDD)

> **Purpose**: Execute TDD Red-Green-Refactor cycle for feature implementation
> **Target**: Coder teammates implementing features with test-first methodology in Agent Teams
> **⚠️ Teammates Only**: This skill is for coder teammates in Agent Teams. Team Lead delegates via teammate spawn.

---

## Quick Start

### When to Use This Skill
- Implement new feature with test coverage
- Fix bug with regression tests
- Refactor code with test safety net

### Quick Reference
```bash
# Red: pytest tests/test_feature.py -k "SC-1"  # FAIL
# Green: [Implement feature]
# Refactor: [Refactor code]
# Verify: pytest  # ALL PASS
```

## What This Skill Covers

### In Scope
- Red-Green-Refactor cycle execution
- Test-first development methodology
- Minimal implementation for Green phase

### Out of Scope
- Test framework selection → @.claude/skills/tdd/REFERENCE.md
- Coverage thresholds → @.claude/skills/ralph-loop/SKILL.md
- Code quality standards → @.claude/skills/vibe-coding/SKILL.md

## Core Concepts

### The TDD Cycle: Red-Green-Refactor

**Phase 1: Red** - Write Failing Test
```python
def test_add_two_numbers():
    result = calculator.add(2, 3)
    assert result == 5
```
Run test → Confirm it FAILS (❌)

**Phase 2: Green** - Minimal Implementation
```python
def add(a, b):
    return a + b  # Just enough to pass
```
Run test → Confirm it PASSES (✅)

**Phase 3: Refactor** - Improve Quality
```python
def add(a: int, b: int) -> int:
    """Add two integers with type safety."""
    return a + b
```
Run ALL tests → Confirm ALL PASS (✅)

### Why TDD Matters
- **Tests drive design**: API designed from usage perspective
- **Regression safety**: Refactor without fear
- **Living documentation**: Tests show intended behavior
- **Fast feedback**: Catch issues immediately

## Further Reading

**Internal**: @.claude/skills/tdd/REFERENCE.md - Advanced TDD concepts, patterns, and examples | @.claude/skills/ralph-loop/SKILL.md - Autonomous completion loop | @.claude/skills/vibe-coding/SKILL.md - Code quality standards | @.claude/skills/tdd/REFERENCE.md - Test framework detection

**External**: [Test-Driven Development by Kent Beck](https://www.amazon.com/Test-Driven-Development-Kent-Beck/dp/0321146530) | [Growing Object-Oriented Software, Guided by Tests](https://www.amazon.com/Growing-Object-Oriented-Software-Guided-Tests/dp/0321503627)

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