NestJS NestJS Testing & Debugging

Question 1

Which testing framework does NestJS use by default for unit and integration tests?

Accepted Answer

Jest

Answer

Mocha

Answer

Jasmine

Answer

Vitest

Question 2

What is the primary purpose of `Test.createTestingModule()` in NestJS?

Accepted Answer

To create an isolated module context for testing

Answer

To start the HTTP server for testing

Answer

To mock all providers automatically

Answer

To run all test suites in parallel

Question 3

Which package must be imported to use `Test.createTestingModule()` in a NestJS test file?

Accepted Answer

@nestjs/testing

Answer

@nestjs/common

Answer

@nestjs/core

Answer

@nestjs/platform-express

Question 4

Which method must be called after `Test.createTestingModule()` to finalize the module for use in tests?

Accepted Answer

.compile()

Answer

.init()

Answer

.bootstrap()

Answer

.build()

Question 5

How do you retrieve a provider instance from a compiled `TestingModule` in NestJS?

Accepted Answer

module.get(ServiceClass)

Answer

module.inject(ServiceClass)

Answer

module.resolve(ServiceClass)

Answer

module.find(ServiceClass)

Question 6

What is the purpose of using `jest.fn()` when defining a mock provider in NestJS unit tests?

Accepted Answer

To create a stub function that records calls and returns undefined by default

Answer

To spy on real implementations without replacing them

Answer

To automatically generate mocks from class metadata

Answer

To wrap an async function in a promise

Question 7

When writing a NestJS unit test for a controller that depends on a service, what is the recommended approach for providing the service?

Accepted Answer

Provide a mock object using `useValue` with jest mock functions

Answer

Import the real service module and let NestJS inject it

Answer

Use `useClass` to provide an alternate real implementation

Answer

Use `useFactory` to instantiate the real service without a database