[player] Add tests for NavigationService

- remove TODO

projects/player/src/app/services/navigation.service.spec.ts

+import { TestBed } from '@angular/core/testing';
+import { NavigationService } from './navigation.service';
+
+describe('NavigationService', () => {
+  let service: NavigationService;
+  beforeEach(() => {
+    TestBed.configureTestingModule({});
+    service = TestBed.inject(NavigationService);
+  });
+
+  it('should be created', () => {
+    expect(service).toBeTruthy();
+  });
+
+  it('pageIndex should be 2', () => {
+    service.pageIndex
+      .subscribe( pageIndex => expect(pageIndex).toEqual(2));
+    service.setPage(2);
+  });
+
+  it('pageIndex should not be 2', () => {
+    service.pageIndex
+      .subscribe( pageIndex => expect(pageIndex).not.toEqual(2));
+    service.setPage(1);
+  });
+});

projects/player/src/app/services/navigation.service.ts

@@ -4,7 +4,7 @@ import { Observable, Subject } from 'rxjs';
 @Injectable({
   providedIn: 'root'
 })
-export class NavigationService { // TODO lohnt für das bischen ein Service?
+export class NavigationService {
   private _pageIndex = new Subject<number>();
 
   setPage(pageIndex: number): void {