sample.service.bed.spec.ts

import { TestBed, inject } from '@angular/core/testing';
import {
  HttpClientTestingModule,
  HttpTestingController
} from '@angular/common/http/testing';
import {
  HttpClient,
} from '@angular/common/http';
import { SampleService } from './sample.service';

const mockAirports = {
  DUB: { name: 'Dublin' },
  WRO: { name: 'Wroclaw' },
  MAD: { name: 'Madrid' }
};

describe('Service: SampleService', () => {
  let httpMock: HttpTestingController;
  let service: SampleService;

  beforeEach(() => {
    TestBed.configureTestingModule({
      imports: [ HttpClientTestingModule ],
      providers: [
        SampleService
      ]
    });
  });

  beforeEach(
    inject([SampleService, HttpTestingController], (_service, _httpMock) => {
      service = _service;
      httpMock = _httpMock;
  }));

  it('fetchAll$: should return a sorted list', () => {
    service.fetchAll$().subscribe(airports => {
      expect(airports.length).toBe(3);
      expect(airports[2][0]).toBe('WRO');
    });

    const req = httpMock.expectOne('https://foo.bar.com/airports');

    req.flush(mockAirports);
    httpMock.verify();
  });

  it('fetchByIATA$: should the selected airport', () => {
    service.fetchByIATA$('MAD').subscribe(airport => {
      expect(airport.name).toBe('Madrid');
    });

    const req = httpMock.expectOne('https://foo.bar.com/airports');

    req.flush(mockAirports);
    httpMock.verify();
  });
});

Great! How to create a testbed for a component with multiple service dependencies?