在已有的单元测试代码，加了这个div标签之后就报错了：
报错：this.service.findFirstFocusable is not a function:
at FocusDirective.get (http://localhost:9876/karma_webpack/src/layout/a11y/keyboard-focus/autofocus/auto-focus.directive.ts:91:25)
从调用栈能看出，FocusDirective实例调用get时，会将控制转角给this.service的findFirstFocusable方法：
解决方法：
· 添加dummy方法：
通过下列代码拿到Angular Test Bed，ATB注入好的Service：
待测试的Component源代码：
@Component({
selector: 'cx-host',
template: ` <div id="a" cxFocus></div>
<div id="b" [cxFocus]="{autofocus: ':host'}"></div> `,
})
class MockComponent {}
单元测试代码：
it('should focus itself', () => {
let service: KeyboardFocusService;
service = TestBed.inject(KeyboardFocusService);
const host = fixture.debugElement.query(By.css('#b'));
const el = host.nativeElement;
spyOn(service, 'findFirstFocusable').and.returnValue(el);
spyOn(el, 'focus').and.callThrough();
fixture.detectChanges();
const event = {
preventDefault: () => {},
stopPropagation: () => {},
};
host.triggerEventHandler('focus', event);
expect(el.focus).toHaveBeenCalled();
expect(service.findFirstFocusable).toHaveBeenCalled();
});
测试结果：
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