Docker Testcontainers Agent Skill

npm install --save-dev testcontainers @testcontainers/postgresql
# Requires a running Docker daemon (Docker Desktop, Colima, or CI's dockerd)
docker info

// tests/cache.integration.test.ts
import { GenericContainer, StartedTestContainer, Wait } from 'testcontainers';
import { createClient, RedisClientType } from 'redis';

describe('rate limiter backed by Redis', () => {
  let container: StartedTestContainer;
  let client: RedisClientType;

  beforeAll(async () => {
    container = await new GenericContainer('redis:7.4-alpine')
      .withExposedPorts(6379)
      .withWaitStrategy(Wait.forLogMessage('Ready to accept connections'))
      .withStartupTimeout(30_000)
      .start();

    client = createClient({
      url: `redis://${container.getHost()}:${container.getMappedPort(6379)}`,
    });
    await client.connect();
  }, 60_000);

  afterEach(async () => {
    await client.flushAll();
  });

  afterAll(async () => {
    await client.quit();
    await container.stop();
  });

  it('blocks the 6th request within a window', async () => {
    for (let i = 0; i < 5; i++) {
      expect(await isAllowed(client, 'user-1')).toBe(true);
    }
    expect(await isAllowed(client, 'user-1')).toBe(false);
  });
});

async function isAllowed(client: RedisClientType, key: string): Promise<boolean> {
  const count = await client.incr(`rl:${key}`);
  if (count === 1) await client.expire(`rl:${key}`, 60);
  return count <= 5;
}

// tests/orders.repository.integration.test.ts
import { PostgreSqlContainer, StartedPostgreSqlContainer } from '@testcontainers/postgresql';
import { Pool } from 'pg';
import { runMigrations } from '../src/db/migrate';
import { OrdersRepository } from '../src/db/orders-repository';

let pg: StartedPostgreSqlContainer;
let pool: Pool;
let repo: OrdersRepository;

beforeAll(async () => {
  pg = await new PostgreSqlContainer('postgres:16-alpine')
    .withDatabase('shop_test')
    .withUsername('shop')
    .withPassword('shop')
    .start();

  pool = new Pool({ connectionString: pg.getConnectionUri() });
  await runMigrations(pool); // the SAME migrations production runs
  repo = new OrdersRepository(pool);
}, 90_000);

beforeEach(async () => {
  await pool.query('TRUNCATE orders RESTART IDENTITY CASCADE');
});

afterAll(async () => {
  await pool.end();
  await pg.stop();
});

it('persists JSONB line items and filters with the @> operator', async () => {
  await repo.create({ customerId: 'c1', items: [{ sku: 'SKU-1', qty: 2 }] });
  await repo.create({ customerId: 'c2', items: [{ sku: 'SKU-9', qty: 1 }] });

  const matches = await repo.findByItemSku('SKU-1'); // uses items @> '[{"sku":"SKU-1"}]'
  expect(matches).toHaveLength(1);
  expect(matches[0].customerId).toBe('c1');
});

// tests/api.e2e.integration.test.ts
import { DockerComposeEnvironment, StartedDockerComposeEnvironment, Wait } from 'testcontainers';

let environment: StartedDockerComposeEnvironment;
let apiBaseUrl: string;

beforeAll(async () => {
  environment = await new DockerComposeEnvironment('.', 'docker-compose.test.yml')
    .withWaitStrategy('api-1', Wait.forHttp('/health', 3000).forStatusCode(200))
    .withWaitStrategy('postgres-1', Wait.forListeningPorts())
    .up(['api', 'postgres']);

  const api = environment.getContainer('api-1');
  apiBaseUrl = `http://${api.getHost()}:${api.getMappedPort(3000)}`;
}, 120_000);

afterAll(async () => {
  await environment.down({ timeout: 10_000 });
});

it('serves orders through the full stack', async () => {
  const created = await fetch(`${apiBaseUrl}/orders`, {
    method: 'POST',
    headers: { 'content-type': 'application/json' },
    body: JSON.stringify({ sku: 'SKU-1', qty: 1 }),
  });
  expect(created.status).toBe(201);

  const list = await fetch(`${apiBaseUrl}/orders`);
  const orders = (await list.json()) as Array<{ sku: string }>;
  expect(orders.map((o) => o.sku)).toContain('SKU-1');
});

// Opt-in reuse keeps the container alive between test runs locally.
// Requires testcontainers.reuse.enable=true in ~/.testcontainers.properties
const pg = await new PostgreSqlContainer('postgres:16-alpine')
  .withDatabase('shop_test')
  .withReuse()
  .start();

// Hand the dynamic URL to the code under test the same way prod config does
process.env.DATABASE_URL = pg.getConnectionUri();

// Copying fixtures and running one-off commands inside a container
const container = await new GenericContainer('postgres:16-alpine')
  .withEnvironment({ POSTGRES_PASSWORD: 'shop' })
  .withCopyFilesToContainer([
    { source: './tests/fixtures/seed.sql', target: '/docker-entrypoint-initdb.d/seed.sql' },
  ])
  .withExposedPorts(5432)
  .start();

const { exitCode, output } = await container.exec(['psql', '-U', 'postgres', '-c', 'SELECT 1']);
expect(exitCode).toBe(0);
expect(output).toContain('1 row');