NestJS Quality Control & Assurance 2

Question 1

Which Jest matcher should you use to verify that a NestJS service method throws a specific exception type?

Accepted Answer

expect(fn).toThrow(NotFoundException)

Answer

toThrow() checks that the function throws an error matching the given class or message when called.

Question 2

When writing an E2E test with Supertest in NestJS, which method initializes the application before the test suite runs?

Accepted Answer

app.init()

Answer

app.init() compiles the module graph and starts the application without binding a port, making it ready for Supertest requests.

Question 3

What is the purpose of the @nestjs/testing package's `overrideGuard` method?

Accepted Answer

To replace a guard with a custom test-only implementation

Answer

overrideGuard() lets you swap a real guard with a mock that returns a fixed canActivate result, isolating the route handler under test.

Question 4

Which database strategy is recommended for NestJS integration tests that need a real database connection without polluting production data?

Accepted Answer

Using an in-memory SQLite instance or a dedicated test database

Answer

An isolated test database or in-memory DB ensures tests are reproducible and don't affect real data.

Question 5

How do you assert that a NestJS controller returns HTTP status 201 in an E2E test using Supertest?

Accepted Answer

.expect(201)

Answer

Supertest's .expect(201) asserts that the HTTP response status code equals 201.

NestJS Practice Test