Integration Testing JavaScript with Docker: Advanced Level

Integration Testing JavaScript with Docker: Advanced Level

Integration testing is a key stage in modern web application development. It allows you to verify the interaction between various system components: the database, cache, external APIs, and the application itself. Docker makes this process predictable, isolated, and reproducible. In this article, we will explore advanced techniques for integration testing JavaScript (Node.js) using Docker.

Why Docker in Integration Testing?

Traditional integration testing faces challenges:

• Differences between developer, CI, and production environments.
• Data pollution in shared databases.
• Complexity of running dependencies (Redis, PostgreSQL, Kafka).

Docker solves these problems by providing lightweight, isolated containers. Each test can launch its own infrastructure, destroying it upon completion. This guarantees clean and repeatable results.

Setting Up a Test Environment with Docker Compose

For advanced testing, we will use a docker-compose.yml that describes all the services needed for tests: the application itself, the database, cache, and mock servers.

Example docker-compose.test.yml:

version: '3.8'services:  app:    build: .    environment:      - NODE_ENV=test      - DB_HOST=postgres_test      - REDIS_HOST=redis_test      - MOCK_SERVER_URL=http://mock-server:8080    depends_on:      - postgres_test      - redis_test      - mock-server    command: ["npm", "run", "test:integration"]

  postgres_test:    image: postgres:15-alpine    environment:      POSTGRES_DB: testdb      POSTGRES_USER: test      POSTGRES_PASSWORD: test    tmpfs: /var/lib/postgresql/data

  redis_test:    image: redis:7-alpine    tmpfs: /data

  mock-server:    image: mockserver/mockserver:latest    environment:      MOCKSERVER_LOG_LEVEL: ERROR

Key points:

• tmpfs: Database and Redis data are stored in RAM, speeding up tests.
• mock-server: An isolated service for simulating external APIs.
• NODE_ENV=test: Switches the application to test configuration.

Writing Integration Tests with Testcontainers

The testcontainers library for Node.js allows you to programmatically manage containers directly from tests. This provides flexibility: you can run specific containers for each test suite.

Installation:

npm install --save-dev testcontainers

Example test with PostgreSQL:

const { GenericContainer } = require('testcontainers');const { Client } = require('pg');

describe('User Repository Integration Test', () => {  let container;  let client;

  beforeAll(async () => {    // Start PostgreSQL container    container = await new GenericContainer('postgres:15-alpine')      .withEnvironment({        POSTGRES_DB: 'testdb',        POSTGRES_USER: 'test',        POSTGRES_PASSWORD: 'test'      })      .withExposedPorts(5432)      .start();

    // Connect to the container    client = new Client({      host: container.getHost(),      port: container.getMappedPort(5432),      database: 'testdb',      user: 'test',      password: 'test'    });    await client.connect();

    // Create schema    await client.query(`      CREATE TABLE users (        id SERIAL PRIMARY KEY,        name VARCHAR(100),        email VARCHAR(100) UNIQUE      )    `);  });

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

  test('should insert and retrieve user', async () => {    await client.query(