Unit testing injectable services

Question

I am having problems while performing a simple unit test in my NX workspace. What I am attempting to do is to 1) configure TestBed and 2) Inject service. However, even if I use scaffolded dummy service, the test still fails as the injected service is said to be undefined

test.service.ts

import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root'
})
export class TestService {
  constructor() { }
}

test.service.spec.ts

import { TestBed } from '@angular/core/testing';
import { TestService } from './test.service';

describe('TestService', () => {
  let service: TestService;
  beforeEach(() => {
    TestBed.configureTestingModule({
      providers: [ TestService ]
    });
    service = TestBed.inject(TestService);
  });
  it('should be created', () => {
    expect(service).toBeTruthy();
  });
});

Does anybody have an idea why is this happening? What exactly is the problem here?

Edit: Yes, I do know I can create a mock. However, the issue still seems strange to me so I would like to get to the bottom of it rather than finding a workaround.

Edit 2: Using ng test <project> --test-file=<filename> directly yields the same results are using NXCLI to perform tests

Edit 3: I shared my code on StackBlitz as requested: https://stackblitz.com/edit/ng-unittest-issue

Answer 1

I've passed through the exact same issues, where the service was undefined when being tested. What solved my problem here were two things:

1. If you are using Jest, make sure you remove jest.mock('@angular/core/testing') from your code. This was required on earlier versions.
2. If you have any other injections on your service, you have to add them to 'providers' under TestBed.configureTestingModule.

Here is a sample functional code and unit testing for a simple Http service, tested on Angular 9 and Angular 10:

api.service.ts

import { HttpClient } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Observable } from 'rxjs';

@Injectable({
  providedIn: 'root',
})
export class ApiService {
  constructor(private http: HttpClient) {}
  baseUrl = 'https://my-api-url.com';

  //api/getId/:id
  getDataById(id: number): Observable<DataSample[]> {
    return this.http.get<DataSample[]>(`${this.baseUrl}/getId/${id}`);
  }
}

export interface DataSample {
  id: number;
  name: string;
}

api.service.spec.ts

import {
  HttpClientTestingModule,
  HttpTestingController,
} from '@angular/common/http/testing';
import { TestBed } from '@angular/core/testing';
import { ApiService, DataSample } from './api.service';

describe('ApiService tests', () => {
  let service: ApiService;
  let httpMock: HttpTestingController;

  beforeEach(() => {
    TestBed.configureTestingModule({
      imports: [HttpClientTestingModule],
      providers: [ApiService],
    });
    service = TestBed.inject(ApiService);
    httpMock = TestBed.inject(HttpTestingController);
  });

  afterEach(() => httpMock.verify());

  it('should return an Observable<DataSample[]>', () => {
    expect(service).toBeTruthy();

    const id: number = 1;
    const mockResult: DataSample[] = [
      {
        id: 1,
        name: 'name1',
      },
      {
        id: 2,
        name: 'name2',
      },
    ];
    const expectedUrl = `https://my-api-url.com/getId/${id}`;

    service
      .getDataById(id)
      .subscribe((res) => expect(res).toBe(mockResult));

    const req = httpMock.expectOne(expectedUrl);
    expect(req.request.method).toBe('GET');
    req.flush(mockResult);
  });
});

Hope it helps 😉