E2E testing with supertest in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this NestJS E2E test using Supertest?

Consider this E2E test snippet for a NestJS controller endpoint that returns a JSON object with a greeting message. What will the test output be when run?

NestJS

return request(app.getHttpServer())
  .get('/hello')
  .expect(200)
  .expect('Content-Type', /json/)
  .expect({ message: 'Hello, world!' });

A Test fails due to a Content-Type mismatch error.

B Test fails with a 404 error because the endpoint '/hello' does not exist.

C Test fails because the response message is different from the expected one.

D Test passes because the response matches the expected JSON and status code.

💡 Hint

Check the expected status code and JSON body in the test.

The test expects a 200 status and a JSON response with the exact message. If the controller returns this correctly, the test passes.

📝 Syntax

intermediate

Which option correctly uses Supertest to test a POST request with JSON body in NestJS?

You want to test a POST endpoint '/users' that accepts a JSON body with a 'name' property. Which code snippet correctly sends the JSON body and expects a 201 status?

A request(app.getHttpServer()).post('/users').body({ name: 'Alice' }).expect(201);

B request(app.getHttpServer()).post('/users').send({ name: 'Alice' }).expect(201);

C request(app.getHttpServer()).post('/users').json({ name: 'Alice' }).expect(201);

D request(app.getHttpServer()).post('/users').set('Content-Type', 'text/plain').send({ name: 'Alice' }).expect(201);

💡 Hint

Supertest uses .send() to send JSON bodies by default.

Option B correctly uses .send() to send JSON and expects status 201. Option B uses .body() which is invalid. Option B uses .json() which is not a Supertest method. Option B sets wrong Content-Type.

🔧 Debug

advanced

Why does this NestJS E2E test with Supertest fail with a timeout?

This test tries to GET '/items' but never completes and times out. What is the most likely cause?

NestJS

it('should return items', () => {
  return request(app.getHttpServer())
    .get('/items')
    .expect(200)
    .expect(res => {
      expect(res.body.length).toBeGreaterThan(0);
    });
});

A The NestJS app was not initialized or started before running the test.

B The test is missing a call to .end() to finish the request.

C The endpoint '/items' returns a 404 causing the test to hang.

D The expect callback throws an error causing the test to timeout.

💡 Hint

Check if the app instance is properly created and listening before tests.

If the NestJS app is not initialized or started, Supertest cannot connect, causing a timeout. The test code itself is correct.

❓ state_output

advanced

What is the value of 'createdUserId' after this E2E test runs?

This test creates a user and saves the returned id in 'createdUserId'. What will be the value of 'createdUserId' after the test?

NestJS

let createdUserId;

it('creates a user', async () => {
  const response = await request(app.getHttpServer())
    .post('/users')
    .send({ name: 'Bob' })
    .expect(201);
  createdUserId = response.body.id;
});

A null because the server returns no content on creation.

B undefined because the response body does not contain 'id'.

C A string or number representing the new user's id returned by the server.

D An error is thrown because 'createdUserId' is not declared.

💡 Hint

Check what the server returns in the response body after creating a user.

The test assigns response.body.id to 'createdUserId'. If the server returns the new user's id, it will be stored correctly.

🧠 Conceptual

expert

Which statement best describes the role of Supertest in NestJS E2E testing?

Choose the most accurate description of how Supertest works within NestJS E2E tests.

A Supertest simulates HTTP requests to the NestJS app's HTTP server to test endpoints as a real client would.

B Supertest mocks NestJS services internally to test controller logic without starting the server.

C Supertest replaces the NestJS HTTP server with a fake server to speed up tests.

D Supertest runs unit tests on individual NestJS components without network calls.

💡 Hint

Think about how E2E tests simulate real user interactions.

Supertest sends real HTTP requests to the running NestJS app server, testing the full request-response cycle.