Mocking providers in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a mock provider for testing.

NestJS

const mockService = { findAll: jest.[1]() };

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

Amock

Bcall

Cfn

DspyOn

Attempts:

3 left

💡 Hint

Common Mistakes

Using jest.mock instead of jest.fn

Using jest.spyOn without an object

Using jest.call which does not exist

jest.fn() creates a mock function that can be used to replace real implementations in tests.

2fill in blank

medium

Complete the code to provide the mock service in the testing module.

NestJS

providers: [{ provide: UserService, use[1]: mockService }],

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

AValue

BClass

CFactory

DExisting

Attempts:

3 left

💡 Hint

Common Mistakes

Using useClass instead of useValue

Using useFactory without a factory function

Using useExisting which references another provider

useValue allows you to provide a specific object or mock as the provider.

3fill in blank

hard

Fix the error in the test setup by completing the missing method to reset mocks.

NestJS

beforeEach(() => { jest.[1](); });

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

ArestoreAllMocks

BresetAllMocks

CresetModules

DclearAllMocks

Attempts:

3 left

💡 Hint

Common Mistakes

Using resetModules which resets the module registry

Using restoreAllMocks which restores original implementations

Using a non-existent resetAllMocks method

jest.clearAllMocks() resets the usage data of mocks between tests.

4fill in blank

hard

Fill both blanks to mock a method and specify its return value.

NestJS

mockService.findAll = jest.[1]().mock[2](['user1', 'user2']);

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

Afn

BmockReturnValue

CmockResolvedValue

DspyOn

Attempts:

3 left

💡 Hint

Common Mistakes

Using spyOn without an object

Using mockResolvedValue for synchronous return

Using mockReturnValue without jest.fn()

jest.fn() creates a mock function, and mockReturnValue sets its return value synchronously.

5fill in blank

hard

Fill all three blanks to create a testing module with a mocked provider and verify the mock was called.

NestJS

const module = await Test.createTestingModule({ providers: [{ provide: UserService, use[1]: mockService }] }).compile(); const service = module.get<UserService>(UserService); await service.findAll(); expect(mockService.findAll).toHaveBeenCalled[2](); jest.[3]();

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

AValue

BOnce

CclearAllMocks

Dmock

Attempts:

3 left

💡 Hint

Common Mistakes

Using useClass instead of useValue

Using toHaveBeenCalled() without once

Not clearing mocks after tests

useValue provides the mock object; toHaveBeenCalledOnce() checks the mock was called once; clearAllMocks resets mocks after test.