Angular 2 单元测试 - @ViewChild 未定义

我正在编写 Angular 2 单元测试。我有一个@ViewChild组件初始化后我需要识别的子组件。在这种情况下，它是一个Timepicker来自 ng2-bootstrap 库的组件，尽管具体细节并不重要。之后我detectChanges()子组件实例仍然未定义。

伪代码：

@Component({
    template: `
        <form>
            <timepicker
                #timepickerChild
                [(ngModel)]="myDate">
            </timepicker>
        </form>
    `
})
export class ExampleComponent implements OnInit {
    @ViewChild('timepickerChild') timepickerChild: TimepickerComponent;
    public myDate = new Date();
}
    
// Spec
describe('Example Test', () => {
    let exampleComponent: ExampleComponent;
    let fixture: ComponentFixture<ExampleComponent>;

    beforeEach(() => {
        TestBed.configureTestingModel({
            // ... whatever needs to be configured
        });
        fixture = TestBed.createComponent(ExampleComponent);
    });

    it('should recognize a timepicker'. async(() => {
        fixture.detectChanges();
        const timepickerChild: Timepicker = fixture.componentInstance.timepickerChild;
        console.log('timepickerChild', timepickerChild)
    }));
});

伪代码按预期工作，直到到达控制台日志。这timepickerChild未定义。为什么会发生这种情况？

我认为应该有效。也许您忘记在配置中导入某些模块。这是完整的测试代码：

import { TestBed, ComponentFixture, async } from '@angular/core/testing';

import { Component, DebugElement } from '@angular/core';
import { FormsModule } from '@angular/forms';

import { ExampleComponent } from './test.component';
import { TimepickerModule, TimepickerComponent } from 'ng2-bootstrap/ng2-bootstrap';

describe('Example Test', () => {
  let exampleComponent: ExampleComponent;
  let fixture: ComponentFixture<ExampleComponent>;

  beforeEach(() => {
    TestBed.configureTestingModule({
      imports: [FormsModule, TimepickerModule.forRoot()],
      declarations: [
        ExampleComponent
      ]
    });
    fixture = TestBed.createComponent(ExampleComponent);
  });

  it('should recognize a timepicker', async(() => {
    fixture.detectChanges();
    const timepickerChild: TimepickerComponent = fixture.componentInstance.timepickerChild;
    console.log('timepickerChild', timepickerChild);
    expect(timepickerChild).toBeDefined();
  }));
});

笨蛋的例子 https://plnkr.co/edit/Hhc3i0KECTs83JTeswHY?p=preview