NestJS NestJS Testing & Debugging 2

Question 1

Which library does NestJS recommend for making HTTP requests in end-to-end (e2e) tests?

Accepted Answer

supertest

Answer

NestJS e2e test scaffolds use `supertest`, which allows you to send HTTP requests directly to an Express/Fastify app without starting a real network server.

Question 2

In a NestJS e2e test, how do you initialize the application before running tests?

Accepted Answer

Call `NestFactory.create()` and `app.init()` inside `beforeAll()`

Answer

For e2e tests you use `NestFactory.create(AppModule)` followed by `app.init()` inside `beforeAll()` so the full application is available to all tests in the suite.

Question 3

What should be called in `afterAll()` at the end of a NestJS e2e test suite?

Accepted Answer

app.close()

Answer

`app.close()` gracefully shuts down the NestJS application and triggers `OnModuleDestroy` lifecycle hooks, preventing open handles from keeping Jest running.

Question 4

How do you override a provider in a NestJS `TestingModule` with a custom mock?

Accepted Answer

builder.overrideProvider(RealService).useValue(mockService)

Answer

`overrideProvider()` is a method on the `TestingModuleBuilder` that lets you swap a registered provider with a mock before calling `.compile()`.

Question 5

What does `jest.spyOn(service, 'methodName')` allow you to do in a NestJS test?

Accepted Answer

Wrap the real method to track calls while still executing the original

Answer

`jest.spyOn()` wraps an existing method so you can assert on calls and optionally override the return value, while the real implementation still runs unless you explicitly mock it.

NestJS Practice Test

NestJS Practice Test

NestJS NestJS Testing & Debugging 2