如何在angular 8中测试window.innerWidth属性？

我在角度和TDD方面比较新。目前，我正在尝试测试一个函数，在调整大小事件期间调用该函数。以下是我的代码：

header.component.ts

@Component({
    selector: 'app-header',
    templateUrl: './header.component.html',
    styleUrls: ['./header.component.scss'],
    host: {
        '(window:resize)': 'onResize($event)'
    }
})
export class HeaderComponent implements OnInit {
    isDesktop = window.innerWidth > 768;
    menuOpen = false;

    constructor() {}

    ngOnInit() {}

    onResize(event) {
        this.isDesktop = event.target.innerWidth > 768;
        this.menuOpen = !this.isDesktop && this.menuOpen;
    }
}

describe('HeaderComponent', () => {
  let component: HeaderComponent;
  let fixture: ComponentFixture<HeaderComponent>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [ HeaderComponent,SideMenuComponent ]
    })
    .compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(HeaderComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

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

  it('should trigger onResize method when window is resized', () => {
    const spyOnResize = spyOn(component, 'onResize');
    window.dispatchEvent(new Event('resize'));
    expect(spyOnResize).toHaveBeenCalled();
  });

header.component.ts

@Component({
    selector: 'app-header',
    templateUrl: './header.component.html',
    styleUrls: ['./header.component.scss'],
    host: {
        '(window:resize)': 'onResize($event)'
    }
})
export class HeaderComponent implements OnInit {
    isDesktop = window.innerWidth > 768;
    menuOpen = false;

    constructor() {}

    ngOnInit() {}

    onResize(event) {
        this.isDesktop = event.target.innerWidth > 768;
        this.menuOpen = !this.isDesktop && this.menuOpen;
    }
}

describe('HeaderComponent', () => {
  let component: HeaderComponent;
  let fixture: ComponentFixture<HeaderComponent>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [ HeaderComponent,SideMenuComponent ]
    })
    .compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(HeaderComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

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

  it('should trigger onResize method when window is resized', () => {
    const spyOnResize = spyOn(component, 'onResize');
    window.dispatchEvent(new Event('resize'));
    expect(spyOnResize).toHaveBeenCalled();
  });

description（'HeaderComponent'，（）=>{
let组件：HeaderComponent；
let夹具：组件夹具；
beforeach（异步（（）=>{
TestBed.configureTestingModule({
声明：[HeaderComponent，SideMenuComponent]
})
.compileComponents（）；
}));
在每个之前（（）=>{
fixture=TestBed.createComponent（HeaderComponent）；
组件=fixture.componentInstance；
fixture.detectChanges（）；
});
它（'应该创建'，（）=>{
expect（component.toBeTruthy（）；
})
它（'调整窗口大小时应触发onResize方法'，（）=>{
const spyOnResize=spyOn（组件“onResize”）；
dispatchEvent（新事件（'resize'））；
期望（spyOnResize）.toHaveBeenCalled（）；
});

当我运行测试时，它会输出测试失败，并说：

：找不到要监视的对象。

。有什么想法或线索可以解决这个问题吗？非常感谢您的帮助。

看看这个答案。看看这个答案。