Estou na aula 10, e não consegui passar pelo teste quando o ID não é informado, dá o erro: Error: Expected null to be truthy. Vou postar todo o spec e ts. Se alguém ver onde estou errando e puder me ajudar, eu agradeço muito.

like-widget.component.spec.ts

describe(LikeWidgetComponent.name, () =>{

    let fixture: ComponentFixture<LikeWidgetComponent> = null;

    beforeEach( async ()=> {
        await TestBed.configureTestingModule({
            imports: [LikeWidgetModule]
        }).compileComponents();

        fixture = TestBed.createComponent(LikeWidgetComponent);

    });    

    it('Should create component' , () => {
        const component = fixture.componentInstance;
        expect(component).toBeTruthy();

    });

    it('Deve gerar ID quando não for informado', () => {
        const component = fixture.componentInstance;
        fixture.detectChanges();
        expect(component.id).toBeTruthy();
    } );

});

LikeWidgetComponent

@Component({
    selector: 'app-like-widget',
    templateUrl: './like-widget.component.html',
    styleUrls: ['like-widget.component.scss']
})
export class LikeWidgetComponent implements OnInit{

    @Output() public liked = new EventEmitter<void>();
    @Input() public likes = 0;
    @Input() public id = null;

    public fonts = { faThumbsUp }

    constructor( private uniqueIdService: UniqueIdService ){}

    public ngOnInit() : void {
        console.log('Aqui', this.id)
        if( !this.id ){
            this.uniqueIdService.generatedUniqueIdWidthPrefix('like-widget');
        }
    }

    public like() : void {
        this.liked.emit();
    }

}