How can I test a class that has a constructor that takes other class objects? (jest)

Question

I'm trying to learn how to unit test for a particular task. Here are some of my files:

//examples.service.ts export class ExamplesService { constructor( @InjectModel(Example.name) private ExampleModel: Model<Example>, private readonly someService: SomeService, private readonly someOtherService: SomeOtherService ){} async findAll(): Promise<Example[]> { return this.exampleModel.find().exec(); } //... other class methods }

//examples.controller.ts @Controller('examples') export class ExamplesController { constructor(private readonly examplesService: ExamplesService) {} @Get() async findAll(): Promise<Example[]> { return this.examplesService.findAll(); } //...

How can i test the functions in examples.service.ts, if it requires me to create a new ExamplesService object that also needs SomeService and SomeOtherService params? Do I create a mock of all of these objects? If so, how?

This is what I have so far:

//examples.controller.spec.ts jest.mock('./examples.service'); describe(ExamplesController, ()=> { let examplesController: ExamplesController; let examplesService: ExamplesService; beforeEach(async () => { const module = TestingModule = await Test.createTestingModule({ controllers: [ExamplesController], providers: [ExamplesService], }).compile(); examplesController = module.get<ExamplesController>(ExamplesController) examplesService = module.get<ExamplesService>(ExamplesService) }) describe('findAll', () => { it('should return all the examples', async () => { let examples = await examplesService.findAll(); expect(examples).resolves.toEqual('some result'); }) }); })

However, when testing findAll, it is unsuccessful because examples always equals to undefined.

Thank you!

web2dev · Accepted Answer · 2021-02-01 13:16:31Z

You need to mock all your dependencies. There are different ways to mock classes. There's some good examples at jest's website https://jestjs.io/docs/en/es6-class-mocks. Not sure what you want to test but can do something like following

 jest.mock('./Model'); const someService = { someMethod: jest.fn().mockReturnValue(Math.random()), someOtherMethod: jest.fn().mockReturnValue({ }), }; const someOtherService = { someMethod: jest.fn().mockReturnValue(Math.random()), }; const examplesService = new ExamplesService(exampleModel as any, someService as any, someOtherService as any);

Thank you! I have a question: why only mock the model, and not someService and someOtherService too? Also I am trying to test the functions in ExampleService, e.g. findAll() returns the correct values
As you can see we are not creating new object for someService and someOtherService . We are mocking 2 methods of someService and then in the ExampleService mocking someService as any. Same applied for someOtherService. There are different ways of mocking a dependency. I have just shown 2 types.
In your test you are mocking the test class. I think you need to create objects for the test class and mock other dependencies. But I could be wrong. There's a similar qs answered here: stackoverflow.com/questions/52878055/…

Collectives™ on Stack Overflow

How can I test a class that has a constructor that takes other class objects? (jest)

1 Answer 1

3 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Linked

Related