EventEmitter订阅单元测试 - Angular 4

Question

以下是我服务的代码

@Injectable()
export class ToolbarService {

/// this event will be subscribed to Detail Component to receive the selected toggle value 
public onToggleValueChangeEvent: EventEmitter<ToggleValueType> = new EventEmitter<ToggleValueType>();

/// This Method will be call from Toolbar Component to raise onToggleValueChangeEvent
 raiseToggleFilterValueChange(toggleValue: ToggleValueType) {
      this.onToggleValueChangeEvent.emit(toggleValue);
    }
}

以下是我的明细组件的代码

@Component({
    selector: 'app--detail',
    templateUrl: './-detail.component.html',
})
export class DetailComponent implements OnInit, OnDestroy {

    constructor(private toolbarService: ToolbarService) {
        this.toolbarService.onToggleValueChangeEvent.subscribe(x => this.onToggleChange(x));
    }

    private onToggleChange(event: ToggleValueType) {
    console.log(event);
        ///Filter with Toggle Value
    }
}

我想为Detail组件编写单元测试。我想要检查onToggleChange应该使用不同的切换值进行调用。但onToggleChange是私有的，所以我必须使用mock onToggleValueChangeEvent来发出。

请帮助:(