Unit testing HttpInterceptor from Angular 4

Question

Can you tell me how to test the HttpInterceptor provided by the Angular 4. I have created an interceptor as per the examples but not sure how to test it. Below is my interce

Answer 1

Just make any call and mock the response with .error() method of HttpTestingController and it should work.

describe('Error interceptor', function () {
let http: HttpTestingController;
  let httpClient: HttpClient;

  beforeEach(() => {
    const testBed = TestBed.configureTestingModule({
      imports: [HttpClientTestingModule],
      providers: [
        {
          provide: HTTP_INTERCEPTORS,
          useClass: MyInterceptor,
          multi: true
        }
      ],
    });

 http = testBed.get(HttpTestingController);
 httpClient = testBed.get(HttpClient);
 });

  it('should catch 401', function (done) {
    httpClient.get('/error').subscribe(() => {}, () => {
      // Perform test
      done();
    });

    http.expectOne('/error').error(new ErrorEvent('Unauthorized error'), {
      status: 401
    });
    http.verify();
  });

});