Тестирование в JavaScript

function sum(a, b) {
  return a + b;
}

describe('sum', () => {
  it('складывает два положительных числа', () => {
    expect(sum(2, 3)).toBe(5);
  });

  it('возвращает число при добавлении нуля', () => {
    expect(sum(5, 0)).toBe(5);
  });

  it('обрабатывает отрицательные числа', () => {
    expect(sum(-1, -2)).toBe(-3);
  });
});

function getUser() {
  return { name: 'Alice', age: 30, tags: ['admin', 'user'] };
}

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

describe('matchers', () => {
  it('toBe: строгое равенство', () => {
    expect(2 + 2).toBe(4);
  });

  it('toEqual: глубокое равенство', () => {
    expect(getUser()).toEqual({ name: 'Alice', age: 30, tags: ['admin', 'user'] });
  });

  it('toContain: включение', () => {
    expect(getUser().tags).toContain('admin');
  });

  it('toThrow: исключение', () => {
    expect(() => divide(10, 0)).toThrow('Division by zero');
  });
});

class UserService {
  notify(user) { console.log(`Notifying ${user.name}`); }

  register(user) {
    this.notify(user);
    return { ...user, registered: true };
  }
}

describe('UserService', () => {
  it('вызывает notify при регистрации', () => {
    const service = new UserService();
    service.notify = jest.fn();

    service.register({ name: 'Alice' });
    service.register({ name: 'Bob' });

    expect(service.notify).toHaveBeenCalled();
    expect(service.notify).toHaveBeenCalledTimes(2);
    expect(service.notify).toHaveBeenCalledWith({ name: 'Alice' });
  });
});

async function fetchPrice(api, productId) {
  const product = await api.getProduct(productId);
  return product.price;
}

describe('fetchPrice', () => {
  it('возвращает цену из ответа API', async () => {
    const mockApi = {
      getProduct: jest.fn().mockResolvedValue({ id: 1, price: 9.99 }),
    };

    const price = await fetchPrice(mockApi, 1);

    expect(price).toBe(9.99);
    expect(mockApi.getProduct).toHaveBeenCalledWith(1);
  });
});

async function loadUser(id, fetch) {
  const res = await fetch(`/users/${id}`);
  if (!res.ok) throw new Error('User not found');
  return res.json();
}

describe('loadUser', () => {
  it('возвращает данные при успехе', async () => {
    const mockFetch = jest.fn().mockResolvedValue({
      ok: true,
      json: () => Promise.resolve({ id: 1, name: 'Alice' }),
    });
    const user = await loadUser(1, mockFetch);
    expect(user).toEqual({ id: 1, name: 'Alice' });
  });

  it('бросает когда ответ не ok', async () => {
    const mockFetch = jest.fn().mockResolvedValue({ ok: false });
    await expect(loadUser(999, mockFetch)).rejects.toThrow('User not found');
  });
});

function delay(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

describe('delay', () => {
  beforeEach(() => jest.useFakeTimers());
  afterEach(() => jest.useRealTimers());

  it('резолвится после задержки', async () => {
    let resolved = false;
    const p = delay(1000).then(() => { resolved = true; });

    expect(resolved).toBe(false);
    jest.runAllTimers();
    await p;
    expect(resolved).toBe(true);
  });
});

class Counter {
  constructor() { this._value = 0; }
  increment() { this._value++; }
  decrement() { this._value--; }
  reset() { this._value = 0; }
  get value() { return this._value; }
}

describe('Counter', () => {
  let counter;

  beforeEach(() => {
    counter = new Counter();
  });

  it('увеличивает', () => {
    counter.increment();
    counter.increment();
    expect(counter.value).toBe(2);
  });

  it('уменьшает', () => {
    counter.increment();
    counter.decrement();
    expect(counter.value).toBe(0);
  });

  it('сбрасывает до нуля', () => {
    counter.increment();
    counter.reset();
    expect(counter.value).toBe(0);
  });
});

class Logger {
  log(msg) { console.log(`[LOG] ${msg}`); }
}

describe('Logger', () => {
  let spy;

  beforeEach(() => {
    spy = jest.spyOn(console, 'log').mockImplementation(() => {});
  });

  afterEach(() => { spy.mockRestore(); });

  it('логирует с префиксом [LOG]', () => {
    const logger = new Logger();
    logger.log('hello');
    expect(spy).toHaveBeenCalledWith('[LOG] hello');
  });
});

function isPalindrome(str) {
  const clean = str.toLowerCase().replace(/[^a-z0-9]/g, '');
  return clean === clean.split('').reverse().join('');
}

describe('isPalindrome', () => {
  test.each([
    ['racecar', true],
    ['hello',   false],
    ['level',   true],
    ['world',   false],
    ['noon',    true],
  ])('%s => %s', (input, expected) => {
    expect(isPalindrome(input)).toBe(expected);
  });
});

async function sendEmail(mailer, to, subject) {
  await mailer.sendMail({ to, subject });
}

describe('sendEmail', () => {
  it('вызывает sendMail с правильными параметрами', async () => {
    const mockMailer = { sendMail: jest.fn().mockResolvedValue(undefined) };

    await sendEmail(mockMailer, '[email protected]', 'Hello');

    expect(mockMailer.sendMail).toHaveBeenCalledWith({
      to: '[email protected]',
      subject: 'Hello',
    });
  });
});