How to test microservices in Replit

You can run multiple processes in a single Repl by using the ampersand (&) operator in your .replit run command. Open .replit (enable 'Show hidden files' in the file tree menu) and configure the run command to start all services simultaneously. Each service runs on a different port, and Replit maps them using the [[ports]] configuration. This approach is simpler than managing separate Repls and keeps all your code in one place.

1# .replit file
2run = "node services/api-gateway/index.js & node services/user-service/index.js & wait"
3
4[[ports]]
5localPort = 3000
6externalPort = 80
7
8[[ports]]
9localPort = 3001
10externalPort = 3001

Open the Shell tab and install a testing framework suitable for your language. For Node.js projects, Jest is the most common choice. For Python projects, pytest works out of the box. The testing framework gives you structured assertions, test runners, and output formatting so you can see exactly which tests pass and which fail.

1# For Node.js projects:
2npm install --save-dev jest
3
4# For Python projects:
5pip install pytest requests

Create a tests directory and add integration test files that make HTTP requests to your running services. Integration tests differ from unit tests because they test the real communication between services — actual HTTP calls, real database queries, and genuine response parsing. Each test should start a request to one service, verify the response, and optionally chain requests across services to test the full flow.

1// tests/integration.test.js
2const API_BASE = 'http://localhost:3000';
3const USER_SERVICE = 'http://localhost:3001';
4
5describe('Microservices Integration', () => {
6  test('API gateway health check returns 200', async () => {
7    const res = await fetch(`${API_BASE}/health`);
8    expect(res.status).toBe(200);
9    const data = await res.json();
10    expect(data.status).toBe('ok');
11  });
12
13  test('User service returns user list', async () => {
14    const res = await fetch(`${USER_SERVICE}/users`);
15    expect(res.status).toBe(200);
16    const users = await res.json();
17    expect(Array.isArray(users)).toBe(true);
18  });
19
20  test('API gateway proxies to user service', async () => {
21    const res = await fetch(`${API_BASE}/api/users`);
22    expect(res.status).toBe(200);
23    const data = await res.json();
24    expect(data).toHaveProperty('users');
25  });
26});

Open package.json and add a test script so you can run all integration tests with a single command. You can also add a test:integration script that specifically targets integration test files, keeping them separate from any unit tests you might have. This makes it easy to run tests from Shell or wire them into your workflow.

1{
2  "scripts": {
3    "start": "node services/api-gateway/index.js & node services/user-service/index.js & wait",
4    "test": "jest",
5    "test:integration": "jest tests/integration"
6  }
7}

Press the Run button to start your services first. Then open a new Shell instance (click the '+' icon in the Shell tab area) and run your test suite. The tests will make HTTP requests to the running services and report results. Running tests in a separate Shell instance lets you keep the services running while iterating on test code. If a test fails, check the Console output from the services for error messages that explain what went wrong.

1# In a separate Shell tab while services are running:
2npm run test:integration

Good integration tests cover both success and error paths. Add tests that send invalid data, missing authentication, or requests to nonexistent endpoints. These tests verify that your services handle errors gracefully and return appropriate HTTP status codes. Error handling is where most inter-service bugs hide, especially when one service expects a response format that another service does not provide.

1// tests/errors.test.js
2describe('Error Handling', () => {
3  test('returns 404 for unknown routes', async () => {
4    const res = await fetch('http://localhost:3000/nonexistent');
5    expect(res.status).toBe(404);
6  });
7
8  test('returns 400 for invalid user data', async () => {
9    const res = await fetch('http://localhost:3001/users', {
10      method: 'POST',
11      headers: { 'Content-Type': 'application/json' },
12      body: JSON.stringify({ name: '' }),
13    });
14    expect(res.status).toBe(400);
15  });
16
17  test('returns 401 for missing auth token', async () => {
18    const res = await fetch('http://localhost:3000/api/protected');
19    expect(res.status).toBe(401);
20  });
21});