How to test a controller with a service that has @Inject in its constructor?

I have a question regarding testing as described on https://docs.nestjs.com/advanced/unit-testing:

beforeEach(async () => {
    const module = await Test.createTestingModule({
        controllers: [CatsController],
        components: [CatsService],
      }).compile();

    catsService = module.get<CatsService>(CatsService);
    catsController = module.get<CatsController>(CatsController);
});

The CatService is quite simple. How about this?

constructor(@Inject(CAT_MODEL_TOKEN) private readonly catModel: Model<Cat>) {}

How are we supposed to provide the catModel to CatsService in beforeEach? Without providing any parameters I get an error:

Nest can’t resolve dependencies of the CatsService. Please verify whether all of them are available in the current context.

[artworkad]

@adrien2p finally 💃 problem solved, thank you so much.

[univerze]

Not sure if it’s still relevant after a year, but when you are unit testing your controller, you don’t want to worry about it’s dependencies so you mock them out by doing:

class MockCatsService {
}
describe('CatsController', () => {

    beforeEach(async () => {
        catsController: CatsController;
        catsService: CatsService;

        const module = await Test.createTestingModule({
            controllers: [CatsController],
            providers: [
                { provide: CatsService, useClass: MockCatsService },
            ],
        }).compile();

        catsService = module.get<CatsService>(CatsService);
        catsController = module.get<CatsController>(CatsController);
    });

});

so when your CatsService changes you don’t have to update it in every single place you use it.