Angular 2单元测试 - @ViewChild未定义

Question

我正在写一个Angular 2单元测试。我有一个@ViewChild子组件，我需要在组件初始化后识别。在这种情况下，它是ng2-bootstrap库中的Timepicker组件，但具体情况无关紧要。在我detectChanges()之后，子组件实例仍未定义。

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，直到您到达控制台日志。 timepickerChild未定义。为什么会这样？

Answer 1

我认为它应该有效。也许您忘记在配置中导入一些模块。以下是完整的测试代码：

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();
  }));
});

Plunker Example

Answer 2

在大多数情况下，只需将其添加到减速状态即可。

beforeEach(async(() => {
        TestBed
            .configureTestingModule({
                imports: [],
                declarations: [TimepickerComponent],
                providers: [],
            })
            .compileComponents() 

Answer 3

确保您的子组件没有评估为false的* ngIf。如果是这样，它将导致子组件未定义。