How do you unit-test a module that uses a dynamic module dependency in NestJS?

0-2 years experience

1. 1You have a NestJS service that depends on a LoggerModule imported via LoggerModule.forRoot({ level: 'debug' }). How would you write a unit test for the service without pulling in the real LoggerModule?
2. 2If you forget to call .compile() on the TestingModule when testing a module that uses a dynamic dependency, what error would you see and how would you fix it?

2-5 years experience

1. 1During a sprint you added ConfigModule.forRoot({ envFilePath: '.env' }) to a feature module, and existing unit tests for a dependent service started failing. Walk me through how you'd debug and adjust the tests.
2. 2Explain the trade‑offs between using Test.createTestingModule with .overrideProvider versus providing a mock implementation directly in the imports array when dealing with a dynamic module.

5-8 years experience

1. 1Our monorepo contains several feature modules that each import a shared dynamic DatabaseModule.forRootAsync(...). We need to keep unit test suites fast. How would you design a testing strategy that isolates each module while avoiding repeated heavy setup?
2. 2When mocking a dynamic module that registers providers based on runtime configuration, what edge cases can cause the mock to diverge from production behavior, and how would you mitigate them?

8+ years experience

1. 1We plan to migrate many existing dynamic modules to a new plugin architecture. From a testing perspective, what changes would you propose to the current unit‑testing approach to ensure long‑term maintainability and cross‑team consistency?
2. 2How would you establish guidelines for mocking dynamic modules across multiple services to prevent hidden coupling and ensure that integration tests still catch configuration errors?