如何让我的Angular5 spyOn按预期工作？

import { TestBed, ComponentFixture } from '@angular/core/testing';
import { MyComponent } from './my.component';

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

  beforeEach(() => {
    TestBed.configureTestingModule({
      declarations: [MyComponent]
    });

    fixture = TestBed.createComponent(MyComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

  it('should call myMethod when button is clicked', () => {
    spyOn(component, 'myMethod');
    const button = fixture.nativeElement.querySelector('button');
    button.click();
    expect(component.myMethod).toHaveBeenCalled();
  });
});