Testing async methods in Angular

I'm writing unit tests with Jasmine in Angular.

export class Component extends AnotherComponent implements OnInit {
  @Input() public configuration: string;
  @Input() public data: Data;
  private _model: IConfiguration;
  public get model(): IConfiguration {
    return this._model;
  }
  constructor(injector: Injector, private _value: Value) {
    super(injector);
  }
  public ngOnInit() {
    super.ngOnInit();
  }
  public async ngOnChanges(changes: SimpleChanges) {
    super.ngOnChanges(changes);
    if (changes && changes['configuration']) {
      this.model = await this.value.doSomething(this.configuration);
    }
  }

I want to test the ngOnChanges() method, specifically the if inside.
This is my test code

describe('Component', () => {
  let component: Component;
  let fixture: ComponentFixture<Component>;
  beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [Module, TranslateModule.forRoot()],
      declarations: [Component]
    })
      .compileComponents();
  }));
  beforeEach(() => {
    fixture = TestBed.createComponent(Component);
    component = fixture.componentInstance;
  });

  it('Expect model to be not undefined', () => {
    const configuration = 'configurationValue';
    component.configuration = configuration;
    component.data = new SampleData();
    fixture.detectCanges();
    expect(component.model).not.toBeUndefined();
  });
});

I do not understand why "component.model" is still undefined. I've also tried with fixture.whenStable() but nothing changed.

it('model exist', (done) => {
    return fixture.whenStable().then(() => {
      fixture.detectChanges();
      expect(component.model).not.toBeUndefined();
      done();
    });

What am I doing wrong? Thanks for the help.