TDD Test Generation - Comprehensive Test-Driven Development Guide

Overview

This skill provides systematic guidance for Test-Driven Development (TDD) combining:

1. RGRC Cycle - Red-Green-Refactor-Commit workflow inspired by t_wada
2. Baby Steps - Incremental development with 2-minute cycles
3. Systematic Test Design - Equivalence partitioning, boundary value analysis, decision tables
4. Test Generation - From SOW test plans to executable test cases

When to Use This Skill

Automatic Triggers

Keywords that activate this skill:

• TDD, Test-Driven Development, テスト駆動開発
• RGRC, Red-Green-Refactor, Baby Steps
• Test generation, test design, test cases
• Equivalence partitioning, boundary value, decision table
• Coverage, test first, unit test

Explicit Invocation

For guaranteed activation:

• "Apply TDD skill"
• "Use TDD test generation skill"
• "Follow RGRC cycle"

Common Scenarios

• Implementing features with /code command
• Generating tests with test-generator agent
• Planning test coverage strategies
• Refactoring with test safety nets
• Reviewing test design quality

Core Concepts

1. Baby Steps - The Foundation

"Make the smallest possible change at each step" - t_wada

Why it matters:

• Immediate error localization (bug is in last 2-minute change)
• Continuous working state (always seconds from green)
• Rapid feedback loop
• Confidence through small successes

2-Minute Cycle:

1. Write smallest failing test (30s)
2. Make it pass minimally (1min)
3. Run tests (10s)
4. Tiny refactor (30s)
5. Commit if green (20s)

2. RGRC Cycle

Goal: "Clean code that works" (動作するきれいなコード) - Ron Jeffries

Red Phase

Write failing test → Verify correct failure reason

Green Phase

Minimal code to pass → "You can sin" (quick/dirty OK)

Refactor Phase

Apply SOLID/DRY → Improve structure → Keep tests green

Commit Phase

All checks pass → Save stable state

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📋 TDD Workflow

Copy this checklist and track your progress:

TDD Cycle:
- [ ] Step 1: Red - 失敗するテスト作成
- [ ] Step 2: Green - 最小限のコードで通過
- [ ] Step 3: Refactor - コード改善
- [ ] Step 4: Commit - 変更をコミット

Step 1: Red - 失敗するテスト作成

// 1. テストファイルを作成/開く
// 2. AAA パターンでテストを書く
test('should validate email format', () => {
  // Arrange
  const email = 'invalid-email'

  // Act
  const result = validateEmail(email)

  // Assert
  expect(result).toBe(false)
})

• テストが意図通りに失敗することを確認
• 失敗理由が正しいことを確認

Step 2: Green - 最小限のコードで通過

• テストを通過する最小限のコードを書く
• この段階では「汚くてもOK」
• テストが緑になることを確認

Step 3: Refactor - コード改善

• コードの重複を除去
• 命名を改善
• 構造を整理
• テストが緑のままであることを確認

Step 4: Commit - 変更をコミット

git add .
git commit -m "feat: add email validation"

• すべてのテストが通過
• リンターエラーがない
• 安定した状態を保存

---

3. Systematic Test Design

Quality > Quantity - Fewer well-designed tests catch more bugs

Equivalence Partitioning

Group inputs with same behavior, test one from each:

// Age validation: <18 (invalid), 18-120 (valid), >120 (invalid)
test('partition 1: rejects 17', () => ...)
test('partition 2: accepts 30', () => ...)
test('partition 3: rejects 121', () => ...)

Boundary Value Analysis

Test edges [min-1, min, max, max+1]:

test('boundary: rejects 17 (18-1)', () => ...)
test('boundary: accepts 18 (min)', () => ...)
test('boundary: accepts 120 (max)', () => ...)
test('boundary: rejects 121 (120+1)', () => ...)

Decision Table Testing

Complex logic with multiple conditions:

// isLoggedIn × isPremium × isActive → canAccess
// Use decision table to cover all combinations systematically

Detailed Knowledge Base

Reference Documents

• [@./references/tdd-rgrc.md] - Complete RGRC cycle guide with t_wada's methodology
• [@./references/test-design.md] - Systematic test design techniques, coverage goals (C0: 80%, C1: 70%), framework-agnostic patterns

Integration Points

With Agents

• test-generator - Generates tests from SOW using this skill's principles
• testability-reviewer - Evaluates test design quality

With Commands

• /code - Applies TDD during implementation
• /test - Validates coverage and quality

Integration Method

# In agent YAML frontmatter
dependencies: [tdd-test-generation]

Or explicit reference:

[@~/.claude/skills/generating-tdd-tests/SKILL.md]

Quick Start

New Feature

1. Red - Write failing test
2. Green - Minimal code
3. Refactor - Clean up
4. Commit - Save
5. Repeat

From SOW

1. Read SOW test plan
2. Apply equivalence partitioning
3. Add boundary values
4. Generate test cases
5. Verify coverage

Refactoring

1. Ensure comprehensive tests
2. Verify green
3. Refactor incrementally
4. Run frequently
5. Commit when green

Best Practices

Do's ✅

• Write test before code
• Keep steps small (Baby Steps)
• Run tests frequently
• Commit when green
• Use systematic test design
• Apply SOLID/DRY in Refactor, not before

Don'ts ❌

• Skip Red phase
• Write multiple tests before any pass
• Refactor without green tests
• Commit with failing tests
• Random test selection
• Complex architecture in Green phase

Coverage Goals

Industry-recommended targets:

• C0 (Statement): 80% minimum
• C1 (Branch): 70% minimum

Why: Cost-benefit balance, focus on critical paths

When NOT to Use TDD

Skip for:

• Prototypes (throwaway code)
• External API integration (use mocks)
• Simple one-off scripts
• UI experiments (visual iteration first)

Success Metrics

TDD is working when:

• Tests written before code (100%)
• Cycles complete in <5 min
• Refactoring feels safe
• Coverage meets targets
• Velocity increases over time

Resources

references/

Comprehensive documentation loaded as needed:

• tdd-rgrc.md - Detailed RGRC cycle implementation
• test-design.md - Complete test design techniques guide

Related Testing Resources

For command output testing and document quality standards:

• ~/.claude/tests/README.md - Command test strategy and verification checklists
• ~/.claude/golden-masters/ - Document quality standards (SOW/Spec examples, output formats)
• ~/.claude/tests/scenarios/ - Test scenarios for command validation

scripts/

Test automation utilities:

• run-tests.sh - Auto-detect package manager and test runner
• coverage-check.sh - Verify coverage thresholds (default: 100%)
• generate-test.sh - Generate test scaffolds with AAA pattern

assets/

Configuration file templates (TDD-optimized with 100% coverage targets):

• vitest.config.ts - Vitest configuration template
• jest.config.js - Jest configuration template