Production Testing Strategy: Unit, Integration with Real DBs, and E2E Confidence

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|                       The Practical Testing Pyramid                   |
|                                                                       |
|     /\      [ E2E Tests ]       -> Critical User Journeys (5-10%)     |
|    /  \     [ Integration Tests] -> Real DB & Service Boundaries (40%) |
|   /____\    [ Unit Tests ]      -> Domain Logic & Pure Invariants (50%)|
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import { PostgreSqlContainer } from '@testcontainers/postgresql';
import { PrismaClient } from '@prisma/client';

describe('OrderService Integration Tests', () => {
  let container: any;
  let prisma: PrismaClient;

  beforeAll(async () => {
    container = await new PostgreSqlContainer().start();
    prisma = new PrismaClient({ datasources: { db: { url: container.getConnectionUri() } } });
    await runMigrations(prisma);
  });

  afterAll(async () => {
    await prisma.$disconnect();
    await container.stop();
  });

  it('should atomically deduct inventory on checkout', async () => {
    const service = new OrderService(prisma);
    const order = await service.createOrder({ productId: 'p1', qty: 2 });
    expect(order.status).toBe('CONFIRMED');

    const updatedStock = await prisma.product.findUnique({ where: { id: 'p1' } });
    expect(updatedStock.stock).toBe(8); // Real DB update verified!
  });
});