Angular 2 unit testing - @ViewChild is undefined

Question

I am writing an Angular 2 unit test. I have a @ViewChild subcomponent that I need to recognize after the component initializes. In this case it's a Timepicker component from the ng2-bootstrap library, though the specifics shouldn't matter. After I detectChanges() the subcomponent instance is still undefined.

Pseudo-code:

@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)
    }));
});

The pseudo-code works as expected until you reach the console log. The timepickerChild is undefined. Why is this happening?

Answer 1

I think it should work. Maybe you forgot to import some module in your configuration. Here is the complete code for test:

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

Make sure your child component does not have a *ngIf that is evaluating to false. If so, it will result in the child component as being undefined.

Answer 3

In most cases just add it to declaration and you are good to go.

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

Answer 4

If you want to test the main component with a stub child component, you need to add a provider to the stub child component; as explained in the article Angular Unit Testing @ViewChild.

import { Component } from '@angular/core';
import { ChildComponent } from './child.component';

@Component({
  selector: 'app-child',
  template: '',
  providers: [
    {
      provide: ChildComponent,
      useClass: ChildStubComponent
    }
  ]
})
export class ChildStubComponent {
  updateTimeStamp() {}
}

Note the providers metadata, to use the class ChildStubComponent when ChildComponent is required.

You can then create your parent component normally, its child will be created with the type ChildStubComponent.