Node.js: テストとデバッグ

npm install --save-dev jest

{
  "scripts": {
    "test": "jest",
    "test:watch": "jest --watch",
    "test:coverage": "jest --coverage"
  }
}

// math.js — テスト対象のモジュール
function add(a, b) {
  return a + b;
}

function subtract(a, b) {
  return a - b;
}

function multiply(a, b) {
  return a * b;
}

function divide(a, b) {
  if (b === 0) throw new Error('Division by zero');
  return a / b;
}

module.exports = { add, subtract, multiply, divide };

// math.test.js
const { add, subtract, multiply, divide } = require('./math');

describe('Math utilities', () => {
  test('add should sum two numbers', () => {
    expect(add(2, 3)).toBe(5);
    expect(add(-1, 1)).toBe(0);
  });

  test('subtract should return the difference', () => {
    expect(subtract(5, 3)).toBe(2);
  });

  test('multiply should return the product', () => {
    expect(multiply(3, 4)).toBe(12);
  });

  test('divide should throw on zero divisor', () => {
    expect(() => divide(10, 0)).toThrow('Division by zero');
  });
});

npm test

 PASS  ./math.test.js
  Math utilities
    ✓ add should sum two numbers (2 ms)
    ✓ subtract should return the difference
    ✓ multiply should return the product
    ✓ divide should throw on zero divisor (1 ms)

Tests:       4 passed, 4 total
Time:        0.5s

// async-functions.js
function fetchUser(id) {
  return new Promise((resolve) => {
    setTimeout(() => {
      resolve({ id, name: `User_${id}` });
    }, 100);
  });
}

async function getUserEmail(id) {
  const user = await fetchUser(id);
  return `${user.name.toLowerCase()}@example.com`;
}

module.exports = { fetchUser, getUserEmail };

// async-functions.test.js
const { fetchUser, getUserEmail } = require('./async-functions');

describe('Async function tests', () => {
  test('fetchUser returns user object', async () => {
    const user = await fetchUser(1);
    expect(user).toEqual({ id: 1, name: 'User_1' });
  });

  test('getUserEmail returns formatted email', async () => {
    const email = await getUserEmail(42);
    expect(email).toBe('user_42@example.com');
  });

  test('fetchUser resolves within 200ms', async () => {
    await expect(fetchUser(1)).resolves.toHaveProperty('id', 1);
  });
});

// email-service.js
class EmailService {
  send(to, subject, body) {
    // 実際のSMTP呼び出し — ユニットテストには遅すぎる
    console.log(`Sending email to ${to}: ${subject}`);
    return true;
  }
}

class UserService {
  constructor(emailService) {
    this.emailService = emailService;
  }

  register(name, email) {
    // ビジネスロジック：検証 + 歓迎メールの送信
    if (!email.includes('@')) throw new Error('Invalid email');
    this.emailService.send(email, 'Welcome', `Hello ${name}!`);
    return { name, email, status: 'registered' };
  }
}

module.exports = { EmailService, UserService };

// email-service.test.js
const { EmailService, UserService } = require('./email-service');

describe('UserService', () => {
  let mockEmailService;
  let userService;

  beforeEach(() => {
    mockEmailService = {
      send: jest.fn().mockReturnValue(true),
    };
    userService = new UserService(mockEmailService);
  });

  test('register should call emailService.send', () => {
    const result = userService.register('Alice', 'alice@example.com');

    expect(result).toEqual({
      name: 'Alice',
      email: 'alice@example.com',
      status: 'registered',
    });

    expect(mockEmailService.send).toHaveBeenCalledWith(
      'alice@example.com',
      'Welcome',
      'Hello Alice!'
    );
  });

  test('register should throw on invalid email', () => {
    expect(() => userService.register('Bob', 'invalid')).toThrow('Invalid email');
    expect(mockEmailService.send).not.toHaveBeenCalled();
  });

  test('register should send exactly one email', () => {
    userService.register('Charlie', 'charlie@example.com');
    expect(mockEmailService.send).toHaveBeenCalledTimes(1);
  });
});

test('basic matchers', () => {
  expect(2 + 2).toBe(4);
  expect({ name: 'Alice' }).toEqual({ name: 'Alice' });
  expect([1, 2, 3]).toContain(2);
  expect('hello world').toMatch(/world/);
  expect(() => { throw new Error('fail'); }).toThrow('fail');
});

npm install --save-dev supertest

// app.js — Expressアプリ（listenせずにエクスポート）
const express = require('express');
const app = express();

app.use(express.json());

let products = [
  { id: 1, name: 'Laptop', price: 999.99 },
  { id: 2, name: 'Phone', price: 499.99 },
];

app.get('/api/products', (req, res) => {
  res.json(products);
});

app.get('/api/products/:id', (req, res) => {
  const product = products.find(p => p.id === parseInt(req.params.id));
  if (!product) return res.status(404).json({ error: 'Product not found' });
  res.json(product);
});

app.post('/api/products', (req, res) => {
  const { name, price } = req.body;
  if (!name || price == null) {
    return res.status(400).json({ error: 'Name and price are required' });
  }
  const newProduct = { id: products.length + 1, name, price };
  products.push(newProduct);
  res.status(201).json(newProduct);
});

module.exports = app;

// app.test.js
const request = require('supertest');
const app = require('./app');

describe('Products API', () => {
  test('GET /api/products should return product list', async () => {
    const response = await request(app).get('/api/products');

    expect(response.status).toBe(200);
    expect(response.body).toHaveLength(2);
    expect(response.body[0]).toHaveProperty('name', 'Laptop');
  });

  test('GET /api/products/:id should return a single product', async () => {
    const response = await request(app).get('/api/products/1');

    expect(response.status).toBe(200);
    expect(response.body.id).toBe(1);
  });

  test('GET /api/products/:id should return 404 for missing product', async () => {
    const response = await request(app).get('/api/products/999');

    expect(response.status).toBe(404);
    expect(response.body).toHaveProperty('error', 'Product not found');
  });

  test('POST /api/products should create a new product', async () => {
    const response = await request(app)
      .post('/api/products')
      .send({ name: 'Tablet', price: 299.99 });

    expect(response.status).toBe(201);
    expect(response.body).toHaveProperty('name', 'Tablet');
    expect(response.body).toHaveProperty('id', 3);
  });

  test('POST /api/products should return 400 for missing fields', async () => {
    const response = await request(app)
      .post('/api/products')
      .send({ name: 'Incomplete Product' });

    expect(response.status).toBe(400);
    expect(response.body).toHaveProperty('error');
  });
});

// protected-routes.test.js
const request = require('supertest');
const app = require('./app');

describe('Protected API routes', () => {
  let token;

  beforeAll(async () => {
    // ログインしてJWTトークンを取得
    const response = await request(app)
      .post('/api/auth/login')
      .send({ username: 'alice', password: 'secret123' });
    token = response.body.token;
  });

  test('should access protected route with valid token', async () => {
    const response = await request(app)
      .get('/api/profile')
      .set('Authorization', `Bearer ${token}`);

    expect(response.status).toBe(200);
    expect(response.body).toHaveProperty('username', 'alice');
  });

  test('should reject access without token', async () => {
    const response = await request(app).get('/api/profile');

    expect(response.status).toBe(401);
  });

  test('should reject access with invalid token', async () => {
    const response = await request(app)
      .get('/api/profile')
      .set('Authorization', 'Bearer invalid_token_here');

    expect(response.status).toBe(401);
  });
});

const request = require('supertest');
const express = require('express');

const app = express();
app.get('/health', (req, res) => res.json({ status: 'ok' }));

describe('GET /health', () => {
  it('returns 200 with status ok', async () => {
    const res = await request(app).get('/health');
    expect(res.status).toBe(200);
    expect(res.body.status).toBe('ok');
  });
});

node inspect app.js

// debug-demo.js
function calculateDiscount(price, memberLevel) {
  debugger; // ここでインスペクタの実行が一時停止する
  let discount = 0;
  if (memberLevel === 'gold') discount = 0.2;
  else if (memberLevel === 'silver') discount = 0.1;
  const finalPrice = price * (1 - discount);
  return finalPrice;
}

console.log(calculateDiscount(100, 'gold'));
console.log(calculateDiscount(100, 'silver'));
console.log(calculateDiscount(100, 'unknown'));

node inspect debug-demo.js

// consoleデバッグのメソッド
const users = [
  { id: 1, name: 'Alice', role: 'admin' },
  { id: 2, name: 'Bob', role: 'user' },
  { id: 3, name: 'Charlie', role: 'admin' },
];

// テーブル表示
console.table(users);

// 実行時間の計測
console.time('database-query');
// ... クエリ処理 ...
console.timeEnd('database-query');

// スタックトレース
console.trace('Where is this called from?');

// グループ化された出力
console.group('User Details');
console.log('Name: Alice');
console.log('Role: admin');
console.groupEnd();

npm install winston
npm install winston-daily-rotate-file

// logger.js
const winston = require('winston');
const DailyRotateFile = require('winston-daily-rotate-file');

const logger = winston.createLogger({
  level: 'info',
  format: winston.format.combine(
    winston.format.timestamp({ format: 'YYYY-MM-DD HH:mm:ss' }),
    winston.format.errors({ stack: true }),
    winston.format.json()
  ),
  defaultMeta: { service: 'my-app' },
  transports: [
    // エラーログ — 別ファイル
    new DailyRotateFile({
      filename: 'logs/error-%DATE%.log',
      datePattern: 'YYYY-MM-DD',
      level: 'error',
      maxSize: '20m',
      maxFiles: '14d',
    }),
    // 全ログ — 統合ファイル
    new DailyRotateFile({
      filename: 'logs/combined-%DATE%.log',
      datePattern: 'YYYY-MM-DD',
      maxSize: '20m',
      maxFiles: '14d',
    }),
  ],
});

// 開発時：コンソールにも色付きで出力
if (process.env.NODE_ENV !== 'production') {
  logger.add(new winston.transports.Console({
    format: winston.format.combine(
      winston.format.colorize(),
      winston.format.simple()
    ),
  }));
}

module.exports = logger;

// app-with-logger.js
const express = require('express');
const logger = require('./logger');

const app = express();
app.use(express.json());

// リクエストロギング用ミドルウェア
app.use((req, res, next) => {
  const start = Date.now();
  res.on('finish', () => {
    const duration = Date.now() - start;
    logger.info('HTTP request', {
      method: req.method,
      url: req.url,
      status: res.statusCode,
      duration: `${duration}ms`,
    });
  });
  next();
});

app.get('/api/health', (req, res) => {
  logger.debug('Health check requested');
  res.json({ status: 'ok', timestamp: new Date().toISOString() });
});

app.get('/api/users/:id', (req, res) => {
  const userId = req.params.id;
  logger.info('User lookup', { userId });

  if (isNaN(userId)) {
    logger.warn('Invalid user ID format', { userId });
    return res.status(400).json({ error: 'Invalid user ID' });
  }

  // ユーザー検索のシミュレーション
  const user = { id: parseInt(userId), name: 'Alice' };
  logger.info('User found', { userId: user.id, name: user.name });
  res.json(user);
});

app.use((err, req, res, next) => {
  logger.error('Unhandled error', { error: err.message, stack: err.stack });
  res.status(500).json({ error: 'Internal server error' });
});

module.exports = app;

{"level":"info","message":"HTTP request","service":"my-app","timestamp":"2026-07-13 10:30:00","method":"GET","url":"/api/users/1","status":200,"duration":"15ms"}
{"level":"warn","message":"Invalid user ID format","service":"my-app","timestamp":"2026-07-13 10:30:05","userId":"abc"}
{"level":"error","message":"Unhandled error","service":"my-app","timestamp":"2026-07-13 10:31:00","error":"Cannot read property 'name' of undefined","stack":"TypeError: Cannot read property..."}

const winston = require('winston');

const logger = winston.createLogger({
  level: 'info',
  format: winston.format.json(),
  transports: [new winston.transports.Console()],
});

logger.info('Server started', { port: 3000, env: 'development' });
logger.warn('Memory usage high', { used: '850MB' });
logger.error('Database connection failed', { db: 'main', retry: 3 });

npm run test:coverage

----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------|---------|----------|---------|---------|-------------------
All files |    90.5 |    85.71 |     100 |    90.5 |
 math.js  |     100 |      100 |     100 |     100 |
 app.js   |   88.24 |    83.33 |     100 |   88.24 | 45-48
----------|---------|----------|---------|---------|-------------------

// string-utils.test.js — 最初にテストを書く（Red）
const { capitalize, truncate, slugify } = require('./string-utils');

describe('StringUtils', () => {
  describe('capitalize', () => {
    test('should capitalize first letter', () => {
      expect(capitalize('hello')).toBe('Hello');
    });

    test('should handle empty string', () => {
      expect(capitalize('')).toBe('');
    });

    test('should handle already capitalized', () => {
      expect(capitalize('Hello')).toBe('Hello');
    });
  });

  describe('truncate', () => {
    test('should truncate long strings', () => {
      expect(truncate('Hello World', 5)).toBe('Hello...');
    });

    test('should not truncate short strings', () => {
      expect(truncate('Hi', 10)).toBe('Hi');
    });
  });

  describe('slugify', () => {
    test('should convert to URL slug', () => {
      expect(slugify('Hello World')).toBe('hello-world');
    });

    test('should handle special characters', () => {
      expect(slugify('C# & .NET!')).toBe('c-and-net');
    });
  });
});

// string-utils.js — テストの後に実装を書く（Green）
function capitalize(str) {
  if (!str) return '';
  return str.charAt(0).toUpperCase() + str.slice(1);
}

function truncate(str, maxLength) {
  if (str.length <= maxLength) return str;
  return str.slice(0, maxLength) + '...';
}

function slugify(str) {
  return str
    .toLowerCase()
    .replace(/[^a-z0-9]+/g, '-')
    .replace(/^-|-$/g, '');
}

module.exports = { capitalize, truncate, slugify };

// tasks-app.js
const express = require('express');
const app = express();
app.use(express.json());

let tasks = [];
let nextId = 1;

function resetTasks() {
  tasks = [];
  nextId = 1;
}

app.get('/api/tasks', (req, res) => {
  const { status, priority } = req.query;
  let filtered = tasks;
  if (status) filtered = filtered.filter(t => t.status === status);
  if (priority) filtered = filtered.filter(t => t.priority === priority);
  res.json(filtered);
});

app.get('/api/tasks/:id', (req, res) => {
  const task = tasks.find(t => t.id === parseInt(req.params.id));
  if (!task) return res.status(404).json({ error: 'Task not found' });
  res.json(task);
});

app.post('/api/tasks', (req, res) => {
  const { title, priority = 'medium' } = req.body;
  if (!title) return res.status(400).json({ error: 'Title is required' });
  const task = { id: nextId++, title, priority, status: 'pending' };
  tasks.push(task);
  res.status(201).json(task);
});

app.patch('/api/tasks/:id', (req, res) => {
  const task = tasks.find(t => t.id === parseInt(req.params.id));
  if (!task) return res.status(404).json({ error: 'Task not found' });
  const { title, status, priority } = req.body;
  if (title) task.title = title;
  if (status) task.status = status;
  if (priority) task.priority = priority;
  res.json(task);
});

app.delete('/api/tasks/:id', (req, res) => {
  const index = tasks.findIndex(t => t.id === parseInt(req.params.id));
  if (index === -1) return res.status(404).json({ error: 'Task not found' });
  const deleted = tasks.splice(index, 1);
  res.json(deleted[0]);
});

module.exports = { app, resetTasks };

// tasks-app.test.js
const request = require('supertest');
const { app, resetTasks } = require('./tasks-app');

beforeEach(() => {
  resetTasks();
});

describe('Tasks API — CRUD operations', () => {
  test('should create a task', async () => {
    const response = await request(app)
      .post('/api/tasks')
      .send({ title: 'Write tests', priority: 'high' });

    expect(response.status).toBe(201);
    expect(response.body).toMatchObject({
      id: 1,
      title: 'Write tests',
      priority: 'high',
      status: 'pending',
    });
  });

  test('should reject task without title', async () => {
    const response = await request(app)
      .post('/api/tasks')
      .send({ priority: 'high' });

    expect(response.status).toBe(400);
    expect(response.body.error).toBe('Title is required');
  });

  test('should list all tasks', async () => {
    await request(app).post('/api/tasks').send({ title: 'Task 1' });
    await request(app).post('/api/tasks').send({ title: 'Task 2' });

    const response = await request(app).get('/api/tasks');
    expect(response.status).toBe(200);
    expect(response.body).toHaveLength(2);
  });

  test('should filter tasks by status', async () => {
    await request(app).post('/api/tasks').send({ title: 'Pending task' });

    const createRes = await request(app).post('/api/tasks').send({ title: 'Done task' });
    await request(app).patch(`/api/tasks/${createRes.body.id}`).send({ status: 'done' });

    const response = await request(app).get('/api/tasks?status=done');
    expect(response.body).toHaveLength(1);
    expect(response.body[0].status).toBe('done');
  });

  test('should update a task', async () => {
    const createRes = await request(app).post('/api/tasks').send({ title: 'Old title' });

    const response = await request(app)
      .patch(`/api/tasks/${createRes.body.id}`)
      .send({ title: 'New title', status: 'done' });

    expect(response.status).toBe(200);
    expect(response.body.title).toBe('New title');
    expect(response.body.status).toBe('done');
  });

  test('should delete a task', async () => {
    const createRes = await request(app).post('/api/tasks').send({ title: 'To delete' });

    const response = await request(app).delete(`/api/tasks/${createRes.body.id}`);
    expect(response.status).toBe(200);

    const listRes = await request(app).get('/api/tasks');
    expect(listRes.body).toHaveLength(0);
  });

  test('should return 404 for non-existent task', async () => {
    const response = await request(app).get('/api/tasks/999');
    expect(response.status).toBe(404);
  });
});

npm test

 PASS  ./tasks-app.test.js
  Tasks API — CRUD operations
    ✓ should create a task (15 ms)
    ✓ should reject task without title (3 ms)
    ✓ should list all tasks (4 ms)
    ✓ should filter tasks by status (8 ms)
    ✓ should update a task (5 ms)
    ✓ should delete a task (5 ms)
    ✓ should return 404 for non-existent task (2 ms)

Tests:       7 passed, 7 total
Time:        0.8s