NestJS Quality Control & Assurance 5

Question 1

Which NestJS health-check library integrates with @nestjs/terminus to verify database connectivity as part of a readiness probe?

Accepted Answer

TypeOrmHealthIndicator from @nestjs/terminus

Answer

TypeOrmHealthIndicator provides a pingCheck() method that tests the database connection and is included in @nestjs/terminus.

Question 2

What testing pattern should be used to verify that a NestJS EventEmitter listener is triggered when a specific event is emitted?

Accepted Answer

Spy on the listener method and emit the event through the EventEmitter2 instance

Answer

Spying on the listener and emitting the event through the real EventEmitter2 instance verifies the full publish-subscribe wiring.

Question 3

When testing a NestJS Microservice consumer, which testing approach avoids requiring a real message broker like RabbitMQ?

Accepted Answer

Inject a mock ClientProxy and assert that send() or emit() was called with correct args

Answer

Mocking ClientProxy isolates the microservice logic from transport concerns, making tests fast and deterministic.

Question 4

How does Pact contract testing complement NestJS E2E tests when multiple microservices are involved?

Accepted Answer

Pact verifies consumer-driven contracts between services without requiring all services to be running simultaneously

Answer

Consumer-driven contract testing lets each service team verify their side of the API contract independently, catching integration issues early.

Question 5

Which approach correctly tests a NestJS middleware function without starting the HTTP server?

Accepted Answer

Call middleware.use() with mock Request, Response, and next function objects

Answer

Middleware functions are plain functions; passing mock req, res, and next objects lets you unit-test the logic directly.

NestJS Practice Test