SKILL: Test-Driven Development (TDD)

Purpose: Execute TDD Red-Green-Refactor cycle for feature implementation Target: Coder Agent implementing features with test-first methodology ⚠️ Subagents Only: This skill is for coder/tester subagents. Main orchestrator must delegate via Task tool.

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

SKILL: Test-Driven Development (TDD)

Quick Start

When to Use This Skill

Quick Reference

What This Skill Covers

In Scope

Out of Scope

Core Concepts

The TDD Cycle: Red-Green-Refactor

Why TDD Matters

Further Reading