Typescript - Angular testing, how to handle http request with parameters that is inside of ngOnInit?

Question

I have a modal component that gets inputs from outside and, when opened, does send a request to server to get data. After getting data it gets assigned to a public variable and used for showing data. How do I write a test for it? Do i need to mock HttpClient? Or do I have to provide all @Input elements and then do a request as normal? But in that case, i need to have real data for back-end to find in database.

I tried googling for this specific problem, but can't seem to find anything. I did found how to mock requests, but not when they are inside of ngOnInit(). I'll add all the necessary code below.

component:

enum Nav {
  General = 'General',
  SSL = 'SSL',
  Routes = 'Routes',
  Statistics = 'Statistics'
};

@Component({
  selector: 'app-mod-route-properties',
  templateUrl: './mod-route-properties.component.html',
  styleUrls: ['./mod-route-properties.component.scss']
})
export class ModRoutePropertiesComponent implements OnInit {

  @Input()
  title: string;

  @Input()
  resourceAddress: ResourceAddress;

  @Input()
  wgsKey: string;

  public emsRouteInfoData: EmsRouteInfoData;

  public sideMenuItems = Object.values(Nav);
  public active: string;
  Nav = Nav;

  constructor(
    private modRoutePropertiesService: ModRoutePropertiesService
  ) {
  }

  ngOnInit() {
    this.active = Nav.General;
    this.modRoutePropertiesService.getRouteProperties(this.resourceAddress, this.wgsKey).subscribe((res: EmsRouteInfoData) => {
      this.emsRouteInfoData = res;
    }, err => {
      console.log(err);
    });
  }
}

service:

@Injectable()
export class ModRoutePropertiesService {

    constructor(
        private urlService: UrlService,
        private serverSettingsService: ServerSettingsService,
        private http: HttpClient
    ) { }

    public getRouteProperties(resourceAddress: ResourceAddress, wgsKey: string) {
        let token = this.urlService.getTokenByKey(wgsKey);
        let url = this.serverSettingsService.getRequestUrl('/route/properties');

        let headers = { 'x-access-token': token };
        let params = {
            manager: resourceAddress.manager,
            node: resourceAddress.node,
            qmgr: resourceAddress.qmgr,
            route: resourceAddress.objectName
        };
        const rq = { headers: new HttpHeaders(headers), params: params };

        return this.http.get<EmsRouteInfoData>(url, rq);
    }
}

test itself:

describe('ModRoutePropertiesComponent', () => {
    let component: ModRoutePropertiesComponent;
    let fixture: ComponentFixture<ModRoutePropertiesComponent>;
    let httpMock: HttpTestingController;

    beforeEach(async(() => {
        TestBed.configureTestingModule({
            imports: [
                FormsModule,
                HttpClientTestingModule,
                NgbModule.forRoot(),
                RouterModule
            ],
            declarations: [
                AppComponent,
                ModRoutePropertiesComponent,
                ModalTitleComponent,
                ModRoutePropertiesGeneralComponent,
                ModRoutePropertiesSslComponent,
                ModRoutePropertiesRoutesComponent,
                ModRoutePropertiesStatisticsComponent,
                ModRoutePropertiesRouteSelectorComponent
            ],
            providers: [
                ModRoutePropertiesService,
                UrlService,
                TabsService,
                {
                    provide: Router,
                    useClass: class { navigate = jasmine.createSpy('tab'); }
                },
                NgbActiveModal,
                ServerSettingsService,
                ModErrorsDisplayService,
                ModalWindowService,
                LoadingIndicatorService
            ]
        })
            .compileComponents();
    }));

    beforeEach(() => {
        fixture = TestBed.createComponent(ModRoutePropertiesComponent);
        component = fixture.componentInstance;
        httpMock = TestBed.get(HttpTestingController);
        fixture.detectChanges();
    });

    it('should create', () => {
        expect(component).toBeTruthy();
    });

    it(`should init 'active'`, () => {
        expect(component.active).toBeDefined();
        expect(component.active).toEqual(component.Nav.General);
    });


    it(`should have initialized 'emsRouteInfoData'`, async(() => {
        expect(component.emsRouteInfoData).toBeDefined();
    }));
});

Answer 1

I did found a solution. So, in order to test a request call, that is inside of ngOnInit method, you need to spy on that specific request function, before ngOnInit is called. Together with spyOn(service, 'function').and.returnValue(Observable.of(object)) it simulates a request call and returns your specified data.
To achieve this, I removed fixture.detectChanges() on beforeEach() test stub. The detechChanges() does trigger a change detection cycle for the component. After that, this is how my beforeEach() looks like:

beforeEach(() => {
        fixture = TestBed.createComponent(ModRoutePropertiesComponent);
        component = fixture.componentInstance;

        resourceAddress = new ResourceAddress();
        resourceAddress.node = 'Node';
        resourceAddress.manager = 'MANAGER';
        resourceAddress.qmgr = 'T1';
        resourceAddress.objectName = 'TestRoute';

        // setting inputs
        component.resourceAddress = resourceAddress;
        component.title = title;
        component.wgsKey = wgsKey;
    });

And after that, I moved detectChanges() to specific test case, after I mock a call to desired function getRouteProperties.

it(`should have initialized 'emsRouteInfoData'`, async(() => {
        // needs 'Observable.of()' to simulate real Observable and subscription to it
        spyOn(service, 'getRouteProperties').and.returnValue(Observable.of(dummyRoute));
        // start ngOnInit
        fixture.detectChanges();
        expect(service.getRouteProperties).toHaveBeenCalled();
        expect(component.emsRouteInfoData).toBeDefined();
    }));