Skip to main content

How to test a structural directive in Angular application

Structural directives influence render of their child view, you definitely have used *ngIf, that is the thing. Steps for testing are quite close to the steps for testing attribute directives: we need to render a custom template and then to assert behavior of the directive.

Let's configure TestBed. The first parameter for MockBuilder is the directive itself, and if it has dependencies we should pass its module as the second parameter:

beforeEach(() => MockBuilder(TargetDirective));

The next step is to render a custom template. Let's assume that the selector of the directive is [target]. Now let's render it in a test:

const fixture = MockRender(  `<div *target="value">    content  </div>`,  {    value: false,  });

Let's assert that the content has not been rendered.

expect(fixture.nativeElement.innerHTML).not.toContain('content');

With help of MockRender we can access the element of the directive via fixture.point to cause events on, and we can change the value via fixture.componentInstance.value.

fixture.componentInstance.value = true;

Because value is true now, the content should be rendered.

fixture.detectChanges();expect(fixture.nativeElement.innerHTML).toContain('content');

Live example#

https://github.com/ike18t/ng-mocks/blob/master/examples/TestStructuralDirective/test.spec.ts
import {  Directive,  Input,  TemplateRef,  ViewContainerRef,} from '@angular/core';import { MockBuilder, MockRender } from 'ng-mocks';
// This directive is the same as `ngIf`,// it renders its content only when its input has truly value.@Directive({  selector: '[target]',})class TargetDirective {  public constructor(    protected templateRef: TemplateRef<any>,    protected viewContainerRef: ViewContainerRef,  ) {}
  @Input() public set target(value: any) {    if (value) {      this.viewContainerRef.createEmbeddedView(this.templateRef);    } else {      this.viewContainerRef.clear();    }  }}
describe('TestStructuralDirectiveWithoutContext', () => {  // Because we want to test the directive, we pass it as the first  // parameter of MockBuilder. We can omit the second parameter,  // because there are no dependencies.  // Do not forget to return the promise of MockBuilder.  beforeEach(() => MockBuilder(TargetDirective));
  it('hides and renders its content', () => {    const fixture = MockRender(      `        <div *target="value">          content        </div>    `,      {        value: false,      },    );
    // Because the value is false the "content" should not be    // rendered.    expect(fixture.nativeElement.innerHTML).not.toContain('content');
    // Let's change the value to true and assert that the "content"    // has been rendered.    fixture.componentInstance.value = true;    fixture.detectChanges();    expect(fixture.nativeElement.innerHTML).toContain('content');
    // Let's change the value to false and assert that the    // "content" has been hidden.    fixture.componentInstance.value = false;    fixture.detectChanges();    expect(fixture.nativeElement.innerHTML).not.toContain('content');  });});