name	generating-tdd-tests
description	TDD with RGRC cycle and Baby Steps methodology. Triggers: TDD, テスト駆動開発, Red-Green-Refactor, Baby Steps, test generation, テスト生成, テスト設計, テストケース, boundary value, 境界値分析, coverage, カバレッジ, unit test
allowed-tools	Read, Write, Edit, Grep, Glob, Task

TDD Test Generation

Purpose

Systematic Test-Driven Development combining RGRC cycle, Baby Steps, and test design techniques.

Baby Steps - 2-Minute Cycle

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

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

Why: Bug is always in last 2-minute change. Always seconds from green.

RGRC Checklist

Copy and track progress:

TDD Cycle:
- [ ] Red - 失敗するテスト作成 (verify correct failure reason)
- [ ] Green - 最小限のコードで通過 (dirty OK)
- [ ] Refactor - コード改善 (keep tests green)
- [ ] Commit - 変更をコミット (all checks pass)

Phase Details

Phase	Goal	Rule
Red	Failing test	Verify failure reason is correct
Green	Pass test	"You can sin" - quick/dirty OK
Refactor	Clean code	Apply SOLID/DRY, keep green
Commit	Save state	All checks pass

Test Design Techniques

Technique	Use For	Example
Equivalence Partitioning	Group inputs with same behavior	Age: <18, 18-120, >120
Boundary Value	Test edges	17, 18, 120, 121
Decision Table	Complex multi-condition logic	isLoggedIn × isPremium → access

Coverage Goals

Level	Target	Focus
C0 (Statement)	80%	All lines executed
C1 (Branch)	70%	All branches taken

Why these targets: Cost-benefit balance, focus on critical paths.

AAA Pattern

test('descriptive name', () => {
  // Arrange - Setup
  // Act - Execute
  // Assert - Verify
})

When NOT to Use TDD

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

Test Priority Matrix

Not everything needs to be tested. Prioritize by impact.

✅ Must Test (Priority 1)

Business Logic: Calculations, validation, state transitions
Service/Repository Layer: Data operations beyond simple CRUD
Critical Paths: Billing, authentication, data persistence
Edge Cases: Boundary values, null/undefined, empty arrays

🟡 Situational (Priority 2)

Utility Functions: Only complex ones
Custom Hooks: State management logic portion
Transformations: Complex mapping/formatting

❌ Skip Testing

Simple property accessors/getters
UI layout/styling
External library behavior verification
Prototype/experimental code
Simple CRUD (framework-provided)
Config file loading

Decision Criteria: "If this logic breaks, will it impact users?"

Naming Convention (Jest/Vitest)

Consistent naming makes test intent clear.

Recommended Pattern

describe('[TargetClass/FunctionName]', () => {
  describe('[MethodName/Scenario]', () => {
    it('when [condition], should [expected result]', () => {
      // Arrange - Act - Assert
    })
  })
})

Examples

describe('PriceCalculator', () => {
  describe('calculateTotal', () => {
    it('when empty array, should return 0', () => {
      expect(calculator.calculateTotal([])).toBe(0)
    })

    it('when discount code applied, should return discounted total', () => {
      const items = [{ price: 1000, quantity: 2 }]
      expect(calculator.calculateTotal(items, 'SAVE10')).toBe(1800)
    })

    it('when tax included, should return total with correct tax', () => {
      const items = [{ price: 1000, quantity: 1 }]
      expect(calculator.calculateTotal(items, null, { includeTax: true })).toBe(1100)
    })
  })
})

Naming Guidelines

Element	Good	Bad
Condition	`when empty array`	`test1`
Expected	`should return 0`	`works correctly`
Context	`when discount applied`	`discount`

Tip: Use descriptive names that serve as documentation

References

Principles (rules/)

@~/.claude/rules/development/TDD_RGRC.md - Full TDD methodology

Skill References

@./references/tdd-rgrc.md - Complete RGRC guide
@./references/test-design.md - Test design techniques

Related Skills

tdd-fundamentals - TDD基本原則
applying-code-principles - コード原則適用

Used by Commands

/code - TDD実装サイクル
/fix - バグ修正のリグレッションテスト
/test - テスト実行・検証

generating-tdd-tests

Install Skill

SKILL.md