Angular 4 Error: No provider for HttpClient

In your test

TestBed.configureTestingModule({
      providers: [FlexSearchService, HttpClientModule]
    });

It should be

TestBed.configureTestingModule({
      imports: [HttpClientModule],
      providers: [FlexSearchService]
    });

or even better (if you want to mock request):

TestBed.configureTestingModule({
      imports: [HttpClientTestingModule],
      providers: [FlexSearchService]
    });