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How to test a structural directive with a context in Angular application

If you did not read "How to test a structural directive", please do it first.

The difference for structural directives with a context in terms of testing is that our custom template has variables.

const fixture = MockRender(  `<div *target="values; let value; let index = myIndex">    {{index}}: {{ value }}  </div>`,  {    values: ['hello', 'world'],  });

This directive simulates behavior of *ngFor. We can do different assertions checking rendered html, and to verify how the directive behaves when we are changing values:

expect(fixture.nativeElement.innerHTML).toContain('0: hello');expect(fixture.nativeElement.innerHTML).toContain('1: world');
fixture.componentInstance.values = ['ng-mocks'];fixture.detectChanges();expect(fixture.nativeElement.innerHTML).toContain('0: ng-mocks');expect(fixture.nativeElement.innerHTML).not.toContain('0: hello');expect(fixture.nativeElement.innerHTML).not.toContain('1: world');

Live example#
import {  Directive,  Input,  TemplateRef,  ViewContainerRef,} from '@angular/core';import { MockBuilder, MockRender } from 'ng-mocks';
export interface ITargetContext {  $implicit: string;  myIndex: number;}
// This directive is almost the same as `ngFor`,// it renders every item as a new row.@Directive({  selector: '[target]',})class TargetDirective {  public constructor(    protected templateRef: TemplateRef<ITargetContext>,    protected viewContainerRef: ViewContainerRef,  ) {}
  @Input() public set target(items: string[]) {    this.viewContainerRef.clear();
    for (let index = 0; index <= items.length; index += 1) {      const value = items[index];      this.viewContainerRef.createEmbeddedView(this.templateRef, {        $implicit: value,        myIndex: index,      });    }  }}
describe('TestStructuralDirectiveWithContext', () => {  // 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('renders passed values', () => {    const fixture = MockRender(      `        <div *target="values; let value; let index = myIndex">        {{index}}: {{ value }}        </div>      `,      {        values: ['hello', 'world'],      },    );
    // Let's assert that the 'values' have been rendered as expected    expect(fixture.nativeElement.innerHTML).toContain('0: hello');    expect(fixture.nativeElement.innerHTML).toContain('1: world');
    // Let's change the 'values' and assert that the new render    // has done everything as expected.    fixture.componentInstance.values = ['ngMocks'];    fixture.detectChanges();    expect(fixture.nativeElement.innerHTML).toContain('0: ngMocks');    expect(fixture.nativeElement.innerHTML).not.toContain('0: hello');    expect(fixture.nativeElement.innerHTML).not.toContain('1: world');  });});