Testing module setup in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the TestingModule in NestJS?

The TestingModule in NestJS creates a test environment that mimics the real module setup. It allows you to isolate and test components like services and controllers with their dependencies.

beginner

Which NestJS function is used to create a TestingModule?

The function Test.createTestingModule() is used to create a TestingModule. It accepts a module metadata object similar to a regular module.

beginner

How do you compile a TestingModule before using it in tests?

You call await module.compile() after creating the TestingModule. This prepares the module and its dependencies for injection and use in tests.

beginner

Why do we use module.get() in NestJS testing?

We use module.get() to retrieve an instance of a provider (like a service) from the TestingModule. This lets us test the provider directly.

intermediate

What is the benefit of isolating dependencies in a TestingModule?

Isolating dependencies lets you test components without relying on real external services or databases. This makes tests faster, more reliable, and easier to understand.

Which method creates a TestingModule in NestJS?

A Test.createTestingModule()

B Module.createTest()

C NestFactory.createTestingModule()

D TestingModule.new()

The correct method is Test.createTestingModule(), which sets up the test module.

What must you call after creating a TestingModule to prepare it for use?

A module.compile()

B module.build()

C module.initialize()

D module.start()

You call module.compile() to finalize the TestingModule setup before using it.

How do you get a service instance from a TestingModule?

A module.retrieve(ServiceClass)

B module.find(ServiceClass)

C module.get(ServiceClass)

D module.fetch(ServiceClass)

Use module.get(ServiceClass) to retrieve the service instance for testing.

Why is it good to mock dependencies in a TestingModule?

A To make tests slower

B To isolate the unit being tested

C To increase external calls

D To avoid writing tests

Mocking dependencies isolates the unit under test, making tests more reliable and faster.

Which of these is NOT part of TestingModule setup?

A Defining providers

B Retrieving instances with get()

C Compiling the module

D Starting the HTTP server

Starting the HTTP server is not part of TestingModule setup; tests run without starting servers.

Explain the steps to set up a TestingModule in NestJS for a service test.

Think about creating, compiling, and getting the service.

Why is isolating dependencies important in NestJS TestingModule setup?

Consider how tests behave with and without real dependencies.