如何在Angular中编写拦截器测试用例

我正在尝试测试Angular 6提供的HttpInterceptor。我已经根据示例创建了一个拦截器，但我无法为下面的拦截器编写测试用例，请指导我完成下面的问题

拦截器 错误

Chrome 75.0.3770（Windows 10.0.0）Lang-interceptor.service应包含内容类型标头失败
TypeError:无法读取null的属性“length”
在HttpHeaders.push../node_modules/@angular/common/fesm5/http.js.HttpHeaders.applyUpdate node_modules/@angular/common/fesm5/http.js:200:1）
在http://localhost:9876/_karma_webpack_/webpack:/node_modules/@angular/common/fesm5/http.js:171:60
在Array.forEach（）处

您的测试是正确的，因为您没有调用在预期时间之前进行http调用的服务

您还可以通过直接http调用扩展您的测试，它应该变成绿色

...
  it('should include a Content-Type header', inject([HttpClient], (http: HttpClient) => {

    const httpOptions = {
      headers: new HttpHeaders({'Content-Type': 'application/json'})
    }

    http.get(environment.baseUrl + 'api/user/login', httpOptions).subscribe();

    const httpRequest = httpMock.expectOne(environment.baseUrl + 'api/user/login');
     // httpRequest.request.headers.delete(InterceptorSkipHeader);

    expect(httpRequest.request.headers.has('Content-Type')).toBe(true);
    expect(httpRequest.request.headers.get('Content-Type')).toBe('application/json');

    httpMock.verify();
  }));
...

---

两天后我就遇到了这个问题。服务拦截HTTP请求应该包括一个内容类型头FAILED TypeError:无法读取的属性'length'null@Krish你是对的，我忘了添加内容类型。检查我编辑的答案。让我检查并告诉结果我仍然面临问题。我用错误消息HMMM更新我的问题，你能用

httpRequest.request.headers.delete（InterceptorSkipHeader）取消行注释吗。这是我在本地考试中唯一没有的。
describe('Lang-interceptor.service', () => {

let httpMock: HttpTestingController;
let interceptor: AutherizationInterceptor;
beforeEach(() => {
    TestBed.configureTestingModule({
        imports: [HttpClientModule, HttpClientTestingModule],
        providers: [{
            provide: HTTP_INTERCEPTORS,
            useClass: AutherizationInterceptor,
            multi: true
        }]
    })
    httpMock = TestBed.get(HttpTestingController);
    interceptor = new AutherizationInterceptor();
});

it('should include a Content-Type header', inject([HttpClient], (http: HttpClient) => {
    const httpOptions = {
      headers: new HttpHeaders({'Content-Type': 'application/json'})
    }
    http.post(environment.baseUrl + 'api/user/login',null, httpOptions).subscribe();
    const httpRequest = httpMock.expectOne(environment.baseUrl + 'api/user/login');
    httpRequest.request.headers.delete(InterceptorSkipHeader);
    expect(httpRequest.request.headers.has('Content-Type')).toBe(true);
    expect(httpRequest.request.headers.get('Content-Type')).toBe('application/json');

    httpMock.verify();
  }));

Chrome 75.0.3770 (Windows 10.0.0) Lang-interceptor.service should include a Content-Type header FAILED
    TypeError: Cannot read property 'length' of null
        at HttpHeaders.push../node_modules/@angular/common/fesm5/http.js.HttpHeaders.applyUpdate node_modules/@angular/common/fesm5/http.js:200:1)
        at http://localhost:9876/_karma_webpack_/webpack:/node_modules/@angular/common/fesm5/http.js:171:60
        at Array.forEach (<anonymous>)

...
  it('should include a Content-Type header', inject([HttpClient], (http: HttpClient) => {

    const httpOptions = {
      headers: new HttpHeaders({'Content-Type': 'application/json'})
    }

    http.get(environment.baseUrl + 'api/user/login', httpOptions).subscribe();

    const httpRequest = httpMock.expectOne(environment.baseUrl + 'api/user/login');
     // httpRequest.request.headers.delete(InterceptorSkipHeader);

    expect(httpRequest.request.headers.has('Content-Type')).toBe(true);
    expect(httpRequest.request.headers.get('Content-Type')).toBe('application/json');

    httpMock.verify();
  }));
...