API Testing

Testing is done using Jest. We will outline the most important files and configurations.

Launching tests

You can launch the tests by running the following command:

cd apps/api && pnpm test

You can also launch the tests in watch mode by running the following command:

cd apps/api && pnpm test:watch

Different kinds of tests

We have two kinds of tests:

• Unit tests
• E2E tests

Unit tests are tests that test a single unit of code. They are named like this: *.service.spec.ts or *.processor.spec.ts.

E2E tests are tests that test the entire application end to end, which means mostly testing your controllers. They are named like this: *.e2e-spec.ts.

Note

If you want to know more about testing in NestJS, you can read the NestJS testing documentation.

Infrastructure setup

We use Testcontainers to mock the infrastructure, mainly for things like databases, redis, etc.

You will find an example of launching the database in the test/test.utils.ts file:

  // Initialize DB with test containers
  postgresContainer = await new PostgreSqlContainer('postgres:16-alpine').start()

  const mikroOrmOptions = createTestMikroOrmOptions({
    allowGlobalContext: true,
    dbName: postgresContainer.getDatabase(),
    host: postgresContainer.getHost(),
    port: postgresContainer.getPort(),
    user: postgresContainer.getUsername(),
    password: postgresContainer.getPassword(),
  })

Note that we use the default mikro-orm configuration for the test database (createTestMikroOrmOptions), but we override the database name, host, port, user and password to use the test container.

You will want to stop the test container at the end of your test suite, and you’ll probably want to clean the database at the beginning of each test.

  // We initialize the NestJS app and the database
  beforeAll(async () => {
    // Initialize the test application (this will launch the test container)
    testContext = await initializeTestApp({
      imports: [PostModule],
    })
    app = testContext.app
    orm = testContext.orm
    em = orm.em.fork()
  })

  // Before each test we clean the database to ensure we start with a fresh state
  beforeEach(async () => {
    await orm.schema.refreshDatabase()
    testUser = await createUserData(em)
    requestWithAuth = initRequestWithAuth(app, testUser.id)
  })

  // After all tests we close the NestJS app and the database, the testcontainer is shut down
  afterAll(async () => {
    await closeTestApp(testContext)
  })

Service mocking

You can mock some services or external services by using the jest.mock function.

Here is an example of mocking the EmailService in the test/test.e2e-setup.ts file.

jest.mock('../modules/email/email.service', () => ({
  EmailService: jest.fn().mockImplementation(() => ({
    sendEmail: jest.fn(),
  })),
}))

// Mocking the ai service example
jest.mock('ai', () => ({
  generateObject: jest.fn().mockResolvedValue({ object: { analysisResult: 'mocked result' } } as never),
}))

// Mock langfuse at module level
jest.mock('langfuse', () => ({
  __esModule: true,
  default: jest.fn().mockImplementation(() => ({
    trace: jest.fn().mockReturnValue({
      span: jest.fn().mockReturnValue({
        end: jest.fn(),
      }),
      update: jest.fn(),
      getTraceUrl: jest.fn(),
    }),
    shutdown: jest.fn(),
  })),
  observeOpenAI: jest.fn((openaiInstance: unknown) => openaiInstance),
}))

Utils and configurations

The test/test.utils.ts file contains some useful utilities for testing, like initializing the test application, creating a test user, and initializing the request with authentication.

The jest.config.ts file contains the Jest configuration for the project. You can customize it to your needs.