Integration testing patterns in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the testing library for integration tests.

Node.js

import [1] from 'supertest';

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

Arequest

Bexpress

Cjest

Dmocha

Attempts:

3 left

💡 Hint

Common Mistakes

Importing the test runner instead of the HTTP request library.

Using 'express' which is the server framework, not the testing tool.

The supertest library is commonly used for integration testing HTTP servers in Node.js. We import it as request to make HTTP calls in tests.

2fill in blank

medium

Complete the code to start the server before running integration tests.

Node.js

beforeAll(async () => {
  server = app.[1](3000);
});

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

Alisten

Bstart

Copen

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like 'start' or 'run' on the app object.

Not starting the server before tests, causing connection errors.

The listen method starts the server on a given port so it can accept requests during tests.

3fill in blank

hard

Fix the error in the test by completing the assertion method.

Node.js

expect(response.status).to[1](200);

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

Aequal

Bbe

CtoBe

Dequals

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'equal' or 'equals' which are not Jest matchers.

Using 'be' which is incomplete and causes syntax errors.

In Jest, the correct matcher to check equality is toBe. Other options are invalid or cause errors.

4fill in blank

hard

Fill both blanks to create a test that sends a POST request with JSON data.

Node.js

await request(app)
  .post('/api/data')
  .set('Content-Type', '[1]')
  .send({ key: 'value' })
  .expect([2]);

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

Aapplication/json

Bapplication/xml

C200

D404

Attempts:

3 left

💡 Hint

Common Mistakes

Setting wrong content type like 'application/xml'.

Expecting wrong status codes causing test failures.

The header Content-Type should be set to application/json when sending JSON data. The expected status code for a successful POST is usually 200.

5fill in blank

hard

Fill all three blanks to write a test that checks the response body for a specific property.

Node.js

test('response has user id', async () => {
  const response = await request(app).get('/user/123');
  expect(response.body).toHaveProperty('[1]');
  expect(typeof response.body.id).to[2]('string');
  expect(response.body.id).not.to[3]('');
});

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

Aid

Bbe

CtoBe

Dequal

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'be' which is not a valid Jest matcher.

Mixing up 'equal' and 'toBe' causing test errors.

The property to check is id. The Jest matcher to check type equality is toBe. To check that the id is not an empty string, use equal with negation.

Practice

1. What is the main goal of integration testing in a Node.js application?

easy

A. To check the syntax of the code

B. To test individual functions in isolation

C. To verify that different parts of the app work together correctly

D. To measure the app's performance under load

Solution

1. Step 1: Understand integration testing purpose

   Integration testing focuses on checking if multiple parts of the app interact correctly, not just individual pieces.

2. Step 2: Compare with other testing types

   Syntax checking is done by linters, unit tests check single functions, and performance tests measure speed, so these are not integration tests.

3. Final Answer:

   To verify that different parts of the app work together correctly -> Option C

4. Quick Check:

   Integration testing = check parts working together [OK]

Hint: Integration tests check combined parts, not single functions [OK]

Common Mistakes:

• Confusing integration tests with unit tests
• Thinking integration tests check code syntax
• Mixing integration tests with performance testing

2. Which of the following is the correct way to define a setup hook in a Node.js integration test using Mocha?

easy

A. init(() => { /* setup code */ })

B. setup(() => { /* setup code */ })

C. start(() => { /* setup code */ })

D. beforeEach(() => { /* setup code */ })

Solution

1. Step 1: Recall Mocha setup hooks

   Mocha uses beforeEach and before hooks to run setup code before tests.

2. Step 2: Identify correct syntax

   Only beforeEach is a valid Mocha hook; setup, init, and start are not Mocha functions.

3. Final Answer:

   beforeEach(() => { /* setup code */ }) -> Option D

4. Quick Check:

   Mocha setup hook = beforeEach [OK]

Hint: Mocha uses beforeEach for setup, not setup or init [OK]

Common Mistakes:

• Using non-existent hook names like setup or init
• Confusing beforeEach with afterEach
• Forgetting arrow function syntax

3. Consider this Node.js integration test snippet using Jest and Supertest:

test('GET /users returns 200', async () => {
  const response = await request(app).get('/users');
  expect(response.statusCode).toBe(200);
});

What does this test check?

medium

A. That the /users endpoint returns a JSON array

B. That the /users endpoint returns a 200 status code

C. That the app throws an error on /users

D. That the /users endpoint is unreachable

Solution

1. Step 1: Analyze the test code

   The test sends a GET request to '/users' and checks the response status code.

2. Step 2: Understand the assertion

   The assertion expects the status code to be 200, meaning success.

3. Final Answer:

   That the /users endpoint returns a 200 status code -> Option B

4. Quick Check:

   Response status 200 means success [OK]

Hint: Check what the expect() function tests in the code [OK]

Common Mistakes:

• Assuming it checks response body instead of status
• Thinking it tests error or unreachable endpoint
• Ignoring async/await usage

4. You wrote this integration test using Jest:

beforeAll(() => {
  db.connect();
});

test('fetch data', async () => {
  const data = await db.getData();
  expect(data).toBeDefined();
});

afterAll(() => {
  db.disconnect();
});

But the test fails because the database connection is not ready. What is the likely problem?

medium

A. beforeAll should be async and await db.connect()

B. afterAll should run before the test

C. db.getData() should not be awaited

D. expect(data).toBeDefined() is incorrect syntax

Solution

1. Step 1: Check async setup in beforeAll

   Database connection is asynchronous, so beforeAll must be async and await db.connect() to ensure readiness.

2. Step 2: Verify other parts

   afterAll runs after tests, awaiting db.getData() is correct, and expect syntax is valid.

3. Final Answer:

   beforeAll should be async and await db.connect() -> Option A

4. Quick Check:

   Async setup needs await in beforeAll [OK]

Hint: Async setup needs await in beforeAll hook [OK]

Common Mistakes:

• Not making beforeAll async for async setup
• Misplacing afterAll before tests
• Ignoring await on async calls

5. You want to write an integration test for a Node.js app that creates a user via POST /users and then fetches it via GET /users/:id. Which pattern best ensures your test is reliable and isolated?

hard

A. Use setup hook to create a test user, then test GET /users/:id, and cleanup hook to delete the user

B. Run both POST and GET requests in the same test without cleanup

C. Only test GET /users/:id assuming user exists in database

D. Manually add user in database before tests and never delete

Solution

1. Step 1: Understand test isolation

   Tests should not depend on external data; setup creates needed data, cleanup removes it.

2. Step 2: Apply setup and cleanup hooks

   Creating a user in setup, testing GET, then deleting user in cleanup keeps tests reliable and repeatable.

3. Final Answer:

   Use setup hook to create a test user, then test GET /users/:id, and cleanup hook to delete the user -> Option A

4. Quick Check:

   Setup and cleanup keep tests isolated and reliable [OK]

Hint: Setup and cleanup hooks keep tests clean and repeatable [OK]

Common Mistakes:

• Not cleaning up test data causing flaky tests
• Assuming data exists without setup
• Combining unrelated tests without isolation