E2E testing with supertest in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Supertest library.

NestJS

import request from '[1]';

Drag options to blanks, or click blank then click option'

Asupertest

Bjest

Cexpress

Dhttp

Attempts:

3 left

💡 Hint

Common Mistakes

Importing 'express' instead of 'supertest'.

Using 'jest' which is a test runner, not for HTTP requests.

The supertest library is imported as request to perform HTTP requests in E2E tests.

2fill in blank

medium

Complete the code to create a NestJS testing module for E2E tests.

NestJS

const moduleRef = await Test.createTestingModule({ imports: [[1]] }).compile();

Drag options to blanks, or click blank then click option'

AHttpModule

BTestingModule

CSupertestModule

DAppModule

Attempts:

3 left

💡 Hint

Common Mistakes

Importing a non-existent module like 'SupertestModule'.

Using 'HttpModule' which is for HTTP clients, not the app module.

In NestJS E2E tests, you import the main AppModule to test the full application.

3fill in blank

hard

Fix the error in the test to correctly send a GET request to '/users'.

NestJS

return request(app.getHttpServer()).[1]('/users').expect(200);

Drag options to blanks, or click blank then click option'

Aput

Bpost

Cget

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'post' or 'put' which are for sending data, not fetching.

Using 'delete' which removes data.

To test a GET request, use the get method of Supertest.

4fill in blank

hard

Fill both blanks to check the response body contains a user with id 1.

NestJS

expect(response.body).toEqual(expect.arrayContaining([expect.objectContaining({ id: [1], name: [2] })]));

Drag options to blanks, or click blank then click option'

A1

B'John'

C'Jane'

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong id like 2 or wrong name like 'Jane'.

Not matching the exact types (number vs string).

The test checks if the response body array contains an object with id 1 and name 'John'.

5fill in blank

hard

Fill all three blanks to send a POST request with JSON body and check status 201.

NestJS

return request(app.getHttpServer()).[1]('/users').send({ name: [2] }).expect([3]);

Drag options to blanks, or click blank then click option'

Apost

B'Alice'

C201

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using GET instead of POST for sending data.

Expecting wrong status code like 200 instead of 201.

Use post to send data, 'Alice' as the name in JSON, and expect HTTP status 201 for resource creation.

Practice

1. What is the main purpose of using supertest in NestJS E2E testing?

easy

A. To style the frontend components

B. To mock database calls inside unit tests

C. To compile TypeScript code before running tests

D. To simulate HTTP requests and test the whole app behavior

Solution

1. Step 1: Understand E2E testing goal

   E2E testing checks the entire app by simulating real HTTP requests and responses.

2. Step 2: Role of supertest in NestJS

   Supertest helps send HTTP requests to the running NestJS app and verify responses, enabling full app behavior testing.

3. Final Answer:

   To simulate HTTP requests and test the whole app behavior -> Option D

4. Quick Check:

   E2E testing = simulate HTTP requests [OK]

Hint: Remember: supertest sends HTTP requests to test app end-to-end [OK]

Common Mistakes:

• Confusing supertest with mocking libraries
• Thinking supertest is for styling or compiling
• Using supertest only for unit tests

2. Which of the following is the correct way to import and use supertest in a NestJS E2E test file?

easy

A. const request = import('supertest');

B. import * as request from 'supertest';

C. import request from 'supertest';

D. const request = require('supertest');

Solution

1. Step 1: Check ES module import style

   In modern NestJS with ES modules, import * as request from 'supertest'; is the correct syntax to import all exports as an object.

2. Step 2: Identify incorrect options

   const request = require('supertest'); uses CommonJS require, which is discouraged in ES module projects. import request from 'supertest'; assumes default export which supertest does not have. const request = import('supertest'); is invalid syntax.

3. Final Answer:

   import * as request from 'supertest'; -> Option B

4. Quick Check:

   Use ES module import * as for supertest [OK]

Hint: Use import * as request from 'supertest' in NestJS E2E tests [OK]

Common Mistakes:

• Using require() instead of import
• Assuming supertest has a default export
• Using dynamic import incorrectly

3. Given this NestJS E2E test snippet, what will be the HTTP status code returned by the test?

const app = await NestFactory.create(AppModule);
await app.init();
return request(app.getHttpServer())
  .get('/users')
  .expect(200);

medium

A. 200

B. 404

C. 500

D. 301

Solution

1. Step 1: Analyze the test request

   The test sends a GET request to '/users' on the initialized app and expects status 200.

2. Step 2: Understand .expect(200) behavior

   The .expect(200) asserts the response status must be 200 for the test to pass.

3. Final Answer:

   200 -> Option A

4. Quick Check:

   Test expects status 200, so response = 200 [OK]

Hint: Check the .expect() status code to predict response [OK]

Common Mistakes:

• Confusing expected status with actual response
• Assuming 404 if route not defined without context
• Ignoring .expect() assertion meaning

4. Identify the error in this NestJS E2E test code snippet:

const app = await NestFactory.create(AppModule);
return request(app.getHttpServer())
  .post('/login')
  .send({ username: 'user', password: 'pass' })
  .expect(201);
await app.close();

medium

A. Using .send() with POST request is invalid

B. Missing await before request call

C. Calling app.close() after return statement

D. Expecting status 201 instead of 200

Solution

1. Step 1: Check code flow with return and await

   The return statement ends the function immediately, so await app.close() after return is unreachable and never runs.

2. Step 2: Identify proper app closing

   To close the app properly, await app.close() must be called before returning the request promise.

3. Final Answer:

   Calling app.close() after return statement -> Option C

4. Quick Check:

   Code after return is unreachable [OK]

Hint: Place app.close() before return to ensure cleanup [OK]

Common Mistakes:

• Ignoring unreachable code after return
• Thinking .send() is invalid for POST
• Assuming status 201 is always wrong

5. You want to write an E2E test in NestJS that sends a POST request with JSON data, verifies the response body contains a specific property, and then closes the app properly. Which code snippet correctly implements this?

hard

A. const app = await NestFactory.create(AppModule);
await app.init();
const response = await request(app.getHttpServer())
.post('/items')
.send({ name: 'item1' })
.expect(201);
expect(response.body).toHaveProperty('id');
await app.close();

B. const app = await NestFactory.create(AppModule);
const response = request(app.getHttpServer())
.post('/items')
.send({ name: 'item1' })
.expect(201);
expect(response.body).toHaveProperty('id');
await app.close();

C. const app = await NestFactory.create(AppModule);
await app.init();
request(app.getHttpServer())
.post('/items')
.send({ name: 'item1' })
.expect(201)
.then(response => {
expect(response.body).toHaveProperty('id');
});
await app.close();

D. const app = await NestFactory.create(AppModule);
await app.init();
const response = await request(app.getHttpServer())
.post('/items')
.send({ name: 'item1' })
.expect(200);
expect(response.body).toHaveProperty('id');
await app.close();

Solution

1. Step 1: Initialize and start the app

   Await NestFactory.create(AppModule) and app.init() to fully bootstrap and start the HTTP server before sending requests.

2. Step 2: Send POST request and await response

   Await the supertest chain request(app.getHttpServer()).post('/items').send({ name: 'item1' }).expect(201) to capture the response object.

3. Step 3: Verify response body and close app

   Assert expect(response.body).toHaveProperty('id') then await app.close() for proper cleanup.

4. Final Answer:

   The snippet with await app.init(), await request.expect(201), body check, and await app.close() -> Option A

5. Quick Check:

   Await init, await request, assert body, await close [OK]

Hint: Always await app.init(), request, and app.close() in E2E tests [OK]

Common Mistakes:

• Not awaiting app.init() before requests
• Not awaiting request call causing missing response
• Expecting wrong status code (200 vs 201)
• Calling app.close() too early or after return