Angular 5 HttpClient HttpTestingController test error path

Question

I have a service that makes a HTTP get request as follows

  public get(uri: string, params?: HttpParams): Observable<Object> {
    return params ? this._http.get(uri, { params: params }) : this._http.get(uri)
      .catch((error: HttpErrorResponse) => this.catchHttpError(error));
  }

  private catchHttpError(error: HttpErrorResponse) : Observable<Object> {
    this._logger.error(`error occurred: ${error.message}`);
    throw(error);
  }

I have a test spec that can test the successful path. How do I:

1. Get the HttpTestingController to error so that the catchHttpError function is called?

2. Test that _httpService.get throws an error back up from the catchHttpError function?

My test so far looks like:

it('should make a get request and catch error', async(inject([HttpService, HttpTestingController], (_httpService: HttpService, backend: HttpTestingController) => {
  spyOn(_httpService, 'get').and.callThrough();
  let actualObjects: Object[] = [];
  _httpService.get('/api/dummy/get/uri').subscribe((objects: Object[]) => {
    actualObjects = objects;
  });

  backend.expectOne('/api/dummy/get/uri').flush(expectedObjects);
  expect(_httpService.get).toHaveBeenCalledTimes(1);
  expect(_httpService.get).toHaveBeenCalledWith('/api/dummy/get/uri');

  expect(actualObjects).toEqual(expectedObjects);
  expect(actualObjects.length).toBe(1);
  //expect(_httpService.get).toThrow();
})));

Answer 1

Ended up going with this.

it('should make a get request and catch error', async(inject([HttpService, HttpTestingController], (_httpService: HttpService, backend: HttpTestingController) => {
  spyOn(_httpService, 'get').and.callThrough();
  let actualObjects: Object[] = [];
  _httpService.get('/api/dummy/get/uri').subscribe(null, (response: HttpErrorResponse) => {
    expect(response.message).toBe('Http failure response for /api/dummy/get/uri: 500 Server Error');
  });

  backend.expectOne('/api/dummy/get/uri').flush(expectedObjects, { status: 500, statusText: 'Server Error' });
  expect(_httpService.get).toHaveBeenCalledTimes(1);
  expect(_httpService.get).toHaveBeenCalledWith('/api/dummy/get/uri');

  expect(actualObjects).toBeNull();
})));