[Angular] Test Directive

directive:

import { Directive, HostListener, HostBinding, ElementRef } from '@angular/core';

@Directive({
  selector: '[credit-card]'
})
export class CreditCardDirective {

  @HostBinding('style.border')
  border: string;

  @HostListener('input', ['$event'])
  onKeyDown(event: KeyboardEvent) {

    const input = event.target as HTMLInputElement;

    let trimmed = input.value.replace(/\s+/g, '');
    if (trimmed.length > ) {
      trimmed = trimmed.substr(, );
    }

    let numbers = [];
    for (let i = ; i < trimmed.length; i += ) {
      numbers.push(trimmed.substr(i, ));
    }

    input.value = numbers.join(' ');

    this.border = '';
    if (/[^\d]+/.test(trimmed)) {
      this.border = '1px solid red';
    }

  }
}

test:

import { DebugElement, Component } from '@angular/core';
import { ComponentFixture, TestBed } from '@angular/core/testing';
import { BrowserDynamicTestingModule, platformBrowserDynamicTesting } from '@angular/platform-browser-dynamic/testing';
import { By } from '@angular/platform-browser';
import { CreditCardDirective } from './credit-card.directive';

TestBed.initTestEnvironment(
  BrowserDynamicTestingModule,
  platformBrowserDynamicTesting()
);

@Component({
  template: `
    <input type="text" [value]="value" credit-card>
  `
})
class TestComponent {
  value = ;
}

describe('CreditCardDirective', () => {

  let component: TestComponent;
  let fixture: ComponentFixture<TestComponent>;
  let el: DebugElement;

  beforeEach(() => {
    TestBed.configureTestingModule({
      declarations: [
        CreditCardDirective,
        TestComponent
      ]
    });
    fixture = TestBed.createComponent(TestComponent);
    component = fixture.componentInstance;
    el = fixture.debugElement;
  });

  it('should format the string with spaces', () => {
    const directive = el.query(By.directive(CreditCardDirective)).nativeElement;
    directive.value = '';
    directive.dispatchEvent(new Event('input'));
    expect(directive.value).toBe('4751 23');
    directive.value = '';
    directive.dispatchEvent(new Event('input'));
    expect(directive.value).toBe('4751 2398 1201 9201');
  });

  it('should have a max-length of 16 characters', () => {
    const directive = el.query(By.directive(CreditCardDirective));
    const directiveEl = directive.nativeElement;
    directiveEl.value = '';
    directiveEl.dispatchEvent(new Event('input'));
    expect(directiveEl.value).toBe('4751 2398 1201 9201');
    directiveEl.value = 'abscdef';
    directiveEl.dispatchEvent(new Event('input'));
    const directiveInstance = directive.injector.get(CreditCardDirective);
    expect(directiveInstance.border).toContain('1px solid red');
  });

});