Angular8 Unittest Router Events - unit-testing

Question

I am trying to test my router event this is what te code in the TS file look like:
constructor(
private router: Router
) {
router.events.subscribe(route => {
// I removed the code because it doesn`t matter for the solution
});
}
unittest:
describe('MainComponent', () => {
let methodSpy: jasmine.Spy;
const eventSubject = new ReplaySubject<RouterEvent>(1);
const routerMock = {
navigate: jasmine.createSpy('navigateByUrl'),
navigateByUrl: jasmine.createSpy('navigateByUrl'),
events: eventSubject.asObservable(),
url: 'test/url',
createUrlTree: (commands, navExtras = {}) => {},
serializeUrl: (commands, navExtras = {}) => {}
}
beforeEach(async(() => {
TestBed.configureTestingModule({
imports: [RouterTestingModule, FormsModule],
declarations: [],
providers: [
{ provide: Router, useValue: routerMock},
{ provide: ActivatedRoute, useValue: routerMock},
]
})
.compileComponents();
}));
beforeEach(() => {
fixture = TestBed.createComponent(MainComponent);
component = fixture.componentInstance;
methodSpy = spyOn(component, 'AdminPanelStarted');
//fixture.detectChanges();
});
it('should trigger the router event and hit the function "Panel"', () => {
eventSubject.next(new NavigationEnd(1, 'test', 'routeUrl'));
expect(methodSpy).toHaveBeenCalled();
});
});
this is the error I am getting:
I can`t find the solution. The only thing I want to test is if the correct function have been called after entering the router.events subscription. The observable is triggered but gives the error that startsWith can not be done on undefined. But what is undefined?
Thx a Lot!