Integration testing Node.js apps

Integration testing means testing a component with multiple sub-components and how they interact. Some sub-components can be external services, databases, and message queues.

External services are running, but their business logic is mocked based on received parameters (request headers, query parameters, etc.). Databases and message queues are spun up using test containers.

This post covers testing service as a component and its API endpoints. This approach can be used with any framework and language. NestJS and Express are used in the examples below.

API endpoints

Below is the controller for two endpoints. First communicates with an external service and retrieves some data based on the sent parameter. The second one retrieves the data from the database.

// users.controller.ts
@Controller('users')
export class UsersController {
  constructor(private userService: UsersService) {}
  @Get()
  async getAll(@Query('type') type: string) {
    return this.userService.findAll(type);
  }
  @Get(':id')
  async getById(@Param('id', new ParseUUIDPipe()) id: string) {
    return this.userService.findById(id);
  }
}

External dependencies

External service is mocked to send data based on the received parameter.

export const createDummyUserServiceServer = async (): Promise<DummyServer> => {
  return createDummyServer((app) => {
    app.get('/users', (req, res) => {
      if (req.query.type !== 'user') {
        return res.status(403).send('User type is not valid');
      }
      res.json(usersResponse);
    });
  });
};

Tests setup

Tests for endpoints can be split into two parts. The first is related to the external dependencies setup.

The example below creates a mocked service and spins up the database using test containers. The environment variables are set for before mentioned dependencies, and the leading service starts running.

The database is cleaned before every test run. External dependencies (mocked service and database) are closed after tests finish.

// test/users.spec.ts
describe('UsersController (integration)', () => {
  let app: INestApplication;
  let dummyUserServiceServerClose: () => void;
  let postgresContainer: StartedTestContainer;
  let usersRepository: Repository<UsersEntity>;
  const databaseConfig = {
    databaseName: 'nestjs-starter-db',
    databaseUsername: 'user',
    databasePassword: 'some-r4ndom-pasS',
    databasePort: 5432,
  }
  beforeAll(async () => {
    const dummyUserServiceServer = await createDummyUserServiceServer();
    dummyUserServiceServerClose = dummyUserServiceServer.close;
    postgresContainer = await new GenericContainer('postgres:15-alpine')
      .withEnvironment({
        POSTGRES_USER: databaseConfig.databaseUsername,
        POSTGRES_PASSWORD: databaseConfig.databasePassword,
        POSTGRES_DB: databaseConfig.databaseName,
      })
      .withExposedPorts(databaseConfig.databasePort)
      .start();
    const moduleFixture: TestingModule = await Test.createTestingModule({
      imports: [AppModule],
    })
      .overrideProvider(ConfigService)
      .useValue({
        get: (key: string): string => {
          const map: Record<string, string | undefined> = process.env;
          map.USER_SERVICE_URL = dummyUserServiceServer.url;
          map.DATABASE_HOSTNAME = postgresContainer.getHost();
          map.DATABASE_PORT = `${postgresContainer.getMappedPort(databaseConfig.databasePort)}`;
          map.DATABASE_NAME = databaseConfig.databaseName;
          map.DATABASE_USERNAME = databaseConfig.databaseUsername;
          map.DATABASE_PASSWORD = databaseConfig.databasePassword;
          return map[key] || '';
        },
      })
      .compile();
    app = moduleFixture.createNestApplication();
    usersRepository = app.get(getRepositoryToken(UsersEntity));
    await app.init();
  });
  beforeEach(async () => {
    await usersRepository.delete({});
  });
  afterAll(async () => {
    await app.close();
    dummyUserServiceServerClose();
    await postgresContainer.stop();
  });
  // ...
});

Tests

The second part covers tests for the implemented endpoints. The first test suite asserts retrieving data from the external service based on the sent type as a query parameter.

// test/users.spec.ts
describe('/users (GET)', () => {
  it('should return list of users', async () => {
    return request(app.getHttpServer())
      .get('/users?type=user')
      .expect(HttpStatus.OK)
      .then((response) => {
        expect(response.body).toEqual(usersResponse);
      });
  });
  it('should throw an error when type is forbidden', async () => {
    return request(app.getHttpServer())
      .get('/users?type=admin')
      .expect(HttpStatus.FORBIDDEN);
  });
});

The second test suite asserts retrieving the data from the database.

// test/users.spec.ts
describe('/users/:id (GET)', () => {
  it('should return found user', async () => {
    const userId = 'b618445a-0089-43d5-b9ca-e6f2fc29a11d';
    const userDetails = {
      id: userId,
      firstName: 'tester',
    };
    const newUser = await usersRepository.create(userDetails);
    await usersRepository.save(newUser);
    return request(app.getHttpServer())
      .get(`/users/${userId}`)
      .expect(HttpStatus.OK)
      .then((response) => {
        expect(response.body).toEqual(userDetails);
      });
  });
  it('should return 404 error when user is not found', async () => {
    const userId = 'b618445a-0089-43d5-b9ca-e6f2fc29a11d';
    return request(app.getHttpServer())
      .get(`/users/${userId}`)
      .expect(HttpStatus.NOT_FOUND);
  });
});

Boilerplate

Here is the link to the boilerplate I use for the development. It contains the examples mentioned above with more details.