Nest.js Can't resolve circular dependency on TestingModule

Question

I have built a new module and service for a Nest app, it has a circular dependency that resolves successfully when I run the application, but when I run the tests, my mockedModule (TestingModule) can't resolve the dependency for the new service I created.

Example of the "LimitsService" created with a circular dependency with "MathService":

@Injectable()
export class LimitsService {
      constructor(
        private readonly listService: ListService,
        @Inject(forwardRef(() => MathService))
        private readonly mathService: MathService,
      ) {}

      async verifyLimit(
        user: User,
        listId: string,
      ): Promise<void> {
         ...
         this.mathService.doSomething()
      }
     
      async someOtherMethod(){...}
}

MathService calls LimitService.someOtherMethod in one of its methods.

This is how the testing module for "MathService" is setup (everything worked fine before without "LimitsService"):

const limitsServiceMock = {
  verifyLimit: jest.fn(),
  someOtherMethod: jest.fn()
};

const listServiceMock = {
  verifyLimit: jest.fn(),
  someOtherMethod: jest.fn()
};

describe('Math Service', () => {

  let mathService: MathService;
  let limitsService: LimitsService;
  let listService: ListService;
  let httpService: HttpService;


  beforeEach(async () => {
    const mockModule: TestingModule = await Test.createTestingModule({
      imports: [HttpModule],
      providers: [
        MathService,
        ConfigService,
        {
          provide: LimitsService,
          useValue: limitsServiceMock
        },
        {
          provide: ListService,
          useValue: listServiceMock
        },
      ],
    }).compile();
    
    httpService = mockModule.get(HttpService);
    limitsService = mockModule.get(LimitsService);
    listService = mockModule.get(ListService);
    mathService= mockModule.get(MathService);
    
 });

...tests

But when I run the test file, I get:

"Nest can't resolve dependencies of the MathService (...). Please make sure that the argument dependency at index [x] is available in the RootTestModule context."

I have tried commenting out "mathService" from "LimitsService" and it works when I do that,but I need mathService.

I have also tried importing "LimitsModule" instead of providing "LimitsService" with forwardRef() and then getting "LimitsService" from mockModule but that threw the same error.

What is the proper way of importing my "LimitsService" into the mockModule?

It seems that LimitsService requires two dependencies, ie, ListService and MathService. However in your code you're not providing ListService as providers. Maybe you can add ListService into your providers list and try again. — 이준형
My mistake when I added the example, in my code I do have ListService listed as a provider — Nicolas Kao

Nicolas Kao Nicolas Kao · Accepted Answer · 2020-09-11T20:08:25

This is now working for me.

SOLUTION

Import jest mock of LimitsService

jest.mock('@Limits/limits.service');

Set Provider with mock

describe('Math Service', () => {

  let mockLimitsService : LimitsService;

  let mathService: MathService;
  let listService: ListService;
  let httpService: HttpService;


  beforeEach(async () => {
    const mockModule: TestingModule = await Test.createTestingModule({
      imports: [HttpModule],
      providers: [
        MathService,
        ConfigService,
        LimitsService,
        {
          provide: ListService,
          useValue: listServiceMock
        },
      ],
    }).compile();

    mockLimitsService = mockModule.get(LimitsService);

    httpService = mockModule.get(HttpService);
    listService = mockModule.get(ListService);
    mathService= mockModule.get(MathService);
    
 });

Nest.js Can't resolve circular dependency on TestingModule

1 Answers

SOLUTION