无法将请求网址与HttpTestingController

Question

我刚刚开始在Angular中编写书写单元测试。首先，我想为我的服务编写测试以从外部服务器获取数据。我试图检查方法的类型。我使用了一些教程，但是无法连接服务器。下面是我的代码。

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

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

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

    service = TestBed.get(GitHubService);
    httpMock = TestBed.get(HttpTestingController);
  });

  it('should create GitHubService', inject(
    [GitHubService],
    (service: GitHubService) => {
      expect(service).toBeTruthy();
    }
  ));

  it('service url should be a GET method', () => {
    const req = httpMock.expectOne(`${service.API_URL}/users`);
    expect(req.request.method).toBe('GET');
  });

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

运行ng test后，结果为1 FAILED, 1 SUCCESS并产生错误：Error: Expected one matching request for criteria "Match URL: https://api.github.com/users", found none.。我一直在寻找答案，但解决方案无法正常工作。我的代码有什么问题，我应该纠正什么？感谢您的建议。