tdd

name	tdd
description	TDD (Test-Driven Development) rules and patterns. Use when: (1) Writing unit tests, (2) Determining test targets, (3) Following TDD cycle. Supports Expo, React Native, React Router, NestJS using Vitest/Jest.

TDD Skill

TDD rules and patterns for Node/TypeScript/React projects.

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Test Target Rules

Priority Order (IMPORTANT)

Exclusions are evaluated FIRST, then Must Test patterns apply.

1. Check Exclusion patterns → If matched, SKIP
2. Check Must Test patterns → If matched, WRITE TEST
3. If neither matched → SKIP (not a test target)

Must Test

Pattern	Description
*.service.ts	Service functions
*.helper.ts, *.util.ts	Helper/utility functions
*.tsx (components)	React components (except paths matching exclusions)
loader, action	Route loaders/actions
*.schema.ts	Zod schemas
use*.ts	Custom hooks

Exclude from Testing (Evaluated First)

Pattern	Reason
**/components/ui/**	shadcn/ui auto-generated (takes priority over *.tsx)
*.d.ts	Type declarations only
**/types.ts, **/types/**	Type definitions only
**/*.port.ts	Interface definitions only
**/index.ts	Barrel files (re-exports)
*.config.ts	Configuration files
**/constants.ts, **/const.ts	Static values only
**/*.css, **/*.scss	Style files

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Naming Convention

Source → Test path mapping:

Source Path	Test Path
app/services/auth.service.ts	__tests__/services/auth.service.test.ts
app/components/Button.tsx	__tests__/components/Button.test.tsx
app/domain/user/user.schema.ts	__tests__/domain/user/user.schema.test.ts

Pattern: Replace root folder with __tests__/ and add .test before extension.

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TDD Cycle

Red → Green → Refactor

1. Red - Write a failing test
2. Green - Write minimal code to pass
3. Refactor - Improve code (keep tests passing)

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AAA Pattern

All tests follow AAA (Arrange-Act-Assert) pattern:

Phase	Role	Example
Arrange	Prepare test data and environment	Mocking, input creation
Act	Execute test target	Function call, event trigger
Assert	Verify results	expect statements

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Framework Test Environment

Framework	Test Runner	Note
Expo	Jest	Vitest NOT supported
React Native	Jest	Vitest NOT supported
React Router v7	Vitest/Jest	Vitest recommended
NestJS	Jest	Official default

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Test Utility Structure

Path	Purpose
__tests__/fixtures/	Mock data builders
__tests__/utils/	Test helper functions

Rules:

1. No inline helpers in test files - use shared locations
2. Check existing utilities before creating new ones
3. Support overrides parameter for customization

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Code Examples

Based on detected framework, read the corresponding reference file (paths relative to .claude/skills/tdd/):

Framework	Reference File
React Router v7	references/react-router.example.md
React Component	references/react-component.example.md
Zod Schema	references/zod-schema.example.md
NestJS	references/nestjs.example.md
Expo/React Native	references/expo-react-native.example.md

Note: Reference examples use English test descriptions for universal accessibility. When writing actual tests, follow the Output Language Rules below.

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Output Language Rules

Item	Language
Test descriptions (it, describe)	Korean
Variable/function names	English
Code comments	Korean

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Quality Checklist

Before completing tests:

• Test file follows naming convention
• All tests have Korean descriptions
• AAA pattern followed
• Mocks initialized in beforeEach
• No any type in test code
• Shared helpers in __tests__/fixtures/ or __tests__/utils/
• All tests pass