munchkin possible async solution - https://stackoverflow.com/questions/60038800/nullinjectorerror-staticinjectorerroraviorbackendservice-nullinjectorerror/60038952#60038952

gistfile1.txt

import {HttpClientTestingModule, HttpTestingController} from '@angular/common/http/testing';
import {inject, TestBed} from '@angular/core/testing';
import {AviorBackendService} from './avior-backend.service';

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

  it('should be created', () => {
    const service: AviorBackendService = TestBed.get(AviorBackendService);
    expect(service).toBeTruthy();
  });

  // Inject the `done` method. This will tell the test suite that asynchronous methods are being called
  // and it will mark the test as failed if within a specific timeout (usually 5s) the `done` is not called
  it('expects service to fetch data with proper sorting', (done) => {
    const service: AviorBackendService = TestBed.get(AviorBackendService);
    // tslint:disable-next-line: prefer-const
    let httpMock: HttpTestingController;
    service.getUserCollection().subscribe(data => {
      expect(data.length).toBe(7);
      const req = httpMock.expectOne('http://localhost:3000/users');
      expect(req.request.method).toEqual('GET');      // Then we set the fake data to be returned by the mock
      req.flush({firstname: 'Chad'});
      done(); // Mark the test as done
    }, done.fail); // Mark the test as failed if something goes wrong
  });
});