Integration vs unit test decision in Express - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a unit test that mocks the database call.

Express

test('should return user data', () => {
  const mockDb = jest.fn().mockReturnValue({ id: 1, name: 'Alice' });
  const result = getUser([1]);
  expect(result.name).toBe('Alice');
});

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

AmockDb

BmockDb()

CdbCall()

DdbCall

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the mock function immediately instead of passing it.

Passing the real database call instead of the mock.

In unit tests, you pass the mock function itself, not its call result, to replace the real database call.

2fill in blank

medium

Complete the code to write an integration test that sends a request to the Express app.

Express

const request = require('supertest');
const app = require('./app');

test('GET /users returns 200', async () => {
  const response = await request(app).[1]('/users');
  expect(response.statusCode).toBe(200);
});

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

Adelete

Bpost

Cput

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using post instead of get for a GET request.

Forgetting to await the request.

To test a GET request, use the get method from supertest.

3fill in blank

hard

Fix the error in the unit test by completing the mock setup correctly.

Express

jest.mock('./db', () => ({
  fetchUser: jest.fn().[1]({ id: 2, name: 'Bob' })
}));

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AmockReturnValue

BmockImplementation

CmockResolvedValue

DmockReturn

Attempts:

3 left

💡 Hint

Common Mistakes

Using mockReturnValue for async functions.

Using a non-existent mockReturn method.

Since fetchUser returns a promise, use mockResolvedValue to mock an async resolved value.

4fill in blank

hard

Fill both blanks to create a test that checks the response body and status code in an integration test.

Express

test('POST /login returns token', async () => {
  const response = await request(app).post('/login').send({ username: 'user', password: 'pass' });
  expect(response.statusCode).toBe([1]);
  expect(response.body).toHaveProperty([2]);
});

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

A200

B'token'

C'error'

D201

Attempts:

3 left

💡 Hint

Common Mistakes

Using status code 201 which means created, not typical for login.

Checking for 'error' property instead of 'token'.

The expected status code for a successful login is 200, and the response body should have a 'token' property.

5fill in blank

hard

Fill all three blanks to write a unit test that mocks a service call and verifies the result.

Express

const service = require('./service');

jest.mock('./service');

test('should return processed data', async () => {
  service.processData.mock[1]({ success: true });
  const result = await processHandler([2]);
  expect(result).toEqual([3]);
});

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

AResolvedValue

B'inputData'

C{ success: true }

DReturnValue

Attempts:

3 left

💡 Hint

Common Mistakes

Using mockReturnValue for async functions.

Passing wrong input data to the handler.

Expecting wrong output object.

Use mockResolvedValue to mock async service calls. Pass the input data string, and expect the mocked success object.