Testing directives

Directives are usually quite straightforward in their overall shape, being components with no view attached. The fact that directives usually work with components gives us a very good idea of how to proceed when testing them.

Consider the copyright.directive.ts file that we created in Chapter 5, Enrich Applications using Pipes and Directives:

import { Directive, ElementRef } from '@angular/core';
@Directive({
  selector: '[appCopyright]'
})
export class CopyrightDirective {
  constructor(el: ElementRef) {
    const currentYear = new Date().getFullYear();
    const targetEl: HTMLElement = el.nativeElement;
    targetEl.classList.add('copyright');
    targetEl.textContent = `Copyright ©${currentYear} All Rights Reserved.`;
  }
}

A directive is usually used in conjunction with a component, so it makes sense to unit test it while using it on a component. Let's create a test host component and add it to...