Testing with Jest & Supertest

import request from 'supertest';
import { app } from '../src/app';
import { prisma } from '../src/lib/prisma';

// Unit test — test a pure function
describe('calculateTotal', () => {
  it('applies discount correctly', () => {
    expect(calculateTotal(100, 20)).toBe(80);  // 20% off
  });

  it('never returns negative total', () => {
    expect(calculateTotal(100, 120)).toBe(0);  // max 100% off
  });
});

// Integration test — test route handler
describe('POST /api/products', () => {
  beforeEach(async () => {
    await prisma.product.deleteMany();  // clean state
  });

  it('creates a product with valid data', async () => {
    const res = await request(app)
      .post('/api/products')
      .set('Authorization', `Bearer ${adminToken}`)
      .send({ name: 'Laptop', price: 45000, categoryId: 'cat1' });

    expect(res.status).toBe(201);
    expect(res.body).toMatchObject({ name: 'Laptop', price: 45000 });
    expect(res.body.id).toBeDefined();
  });

  it('returns 400 for invalid data', async () => {
    const res = await request(app)
      .post('/api/products')
      .set('Authorization', `Bearer ${adminToken}`)
      .send({ name: '' });  // invalid

    expect(res.status).toBe(400);
    expect(res.body.errors).toBeDefined();
  });
});

import request from 'supertest';
import { app } from '../src/app';

// Mock external services
jest.mock('../src/lib/payment', () => ({
  processPayment: jest.fn().mockResolvedValue({ id: 'pay_123', status: 'success' }),
}));

jest.mock('../src/lib/email', () => ({
  sendOrderConfirmation: jest.fn().mockResolvedValue(true),
}));

describe('Order Creation', () => {
  let authToken: string;
  let productId: string;

  beforeAll(async () => {
    // Create test user and product
    const user = await prisma.user.create({ data: testUser });
    authToken = generateToken(user.id);
    const product = await prisma.product.create({ data: { ...testProduct, stock: 10 } });
    productId = product.id;
  });

  it('creates order and reduces stock', async () => {
    const res = await request(app)
      .post('/api/orders')
      .set('Authorization', `Bearer ${authToken}`)
      .send({ productId, quantity: 2, addressId: 'addr_1' });

    expect(res.status).toBe(201);
    expect(res.body.status).toBe('confirmed');

    // Verify stock was reduced
    const product = await prisma.product.findUnique({ where: { id: productId } });
    expect(product!.stock).toBe(8); // 10 - 2

    // Verify email was sent
    expect(sendOrderConfirmation).toHaveBeenCalledWith(
      expect.objectContaining({ orderId: res.body.id })
    );
  });

  afterAll(async () => {
    await prisma.user.deleteMany();
    await prisma.product.deleteMany();
    await prisma.$disconnect();
  });
});