Integration Testing TypeScript with Docker: Complete Guide

Introduction: Why You Need TypeScript Integration Testing with Docker

Integration testing is a key development stage that checks the interaction between different modules of your application. Unlike unit tests, which isolate a single component, integration tests verify how the database, API, external services, and business logic work together.

Using Docker in TypeScript integration testing solves several problems:

• Environment isolation — tests run in identical conditions on all machines
• Dependency management — databases, queues, and caches are started automatically
• Reproducibility — tests produce the same results locally and in CI/CD
• Fast recovery — containers are recreated in seconds

In this article, we will walk through a practical example of setting up integration testing for a TypeScript application using Docker, Jest, and Supertest.

1. Project Setup and Dependency Installation

Let's start by creating a basic TypeScript project. Make sure you have Node.js (v18+) and Docker installed.

mkdir typescript-docker-testingcd typescript-docker-testingnpm init -ynpm install express typescript ts-node @types/node @types/expressnpm install --save-dev jest ts-jest @types/jest supertest @types/supertest

Create tsconfig.json:

{  "compilerOptions": {    "target": "ES2020",    "module": "commonjs",    "outDir": "./dist",    "rootDir": "./src",    "strict": true,    "esModuleInterop": true,    "skipLibCheck": true  },  "include": ["src/**/*"],  "exclude": ["node_modules", "**/*.test.ts"]}

Configure Jest in package.json:

"jest": {  "preset": "ts-jest",  "testEnvironment": "node",  "testMatch": ["**/*.test.ts"]}

2. Creating a Simple Express Application

Let's create the folder structure and a simple application that will interact with a PostgreSQL database.

mkdir srcmkdir src/configmkdir src/modelsmkdir src/routesmkdir src/__tests__

src/config/database.ts — database connection configuration:

import { Pool } from 'pg';

const pool = new Pool({  host: process.env.DB_HOST || 'localhost',  port: Number(process.env.DB_PORT) || 5432,  database: process.env.DB_NAME || 'testdb',  user: process.env.DB_USER || 'testuser',  password: process.env.DB_PASSWORD || 'testpass'});

export default pool;

src/app.ts — main application:

import express from 'express';import userRoutes from './routes/users';

const app = express();app.use(express.json());app.use('/api/users', userRoutes);

export default app;

src/index.ts — entry point:

import app from './app';

const PORT = process.env.PORT || 3000;app.listen(PORT, () => {  console.log(`Server running on port ${PORT}`);});

src/routes/users.ts — simple user route:

import { Router, Request, Response } from 'express';import pool from '../config/database';

const router = Router();

router.get('/', async (req: Request, res: Response) => {  try {    const result = await pool.query('SELECT * FROM users');    res.json(result.rows);  } catch (error) {    res.status(500).json({ error: 'Database error' });  }});

router.post('/', async (req: Request, res: Response) => {  const { name, email } = req.body;  try {    const result = await pool.query(      'INSERT INTO users (name, email) VALUES ($1, $2) RETURNING *',      [name, email]    );    res.status(201).json(result.r
```