Component:

import { Component, Input, ChangeDetectionStrategy, EventEmitter, Output } from [email protected]/core‘;

@Component({
  selector: ‘stock-counter‘,
  changeDetection: ChangeDetectionStrategy.OnPush,
  template: `
    <div class="stock-counter">
      <div>
        <
 
div 
          (keydown)="onKeyUp($event)"
          (blur)="onBlur($event)"
          (focus)="onFocus($event)"
          tabindex="0">
          <p>{{ value }}</p>
          <div tabindex="-1">
            <button type="button" tabindex="-1" (click)="increment()" [disabled]
 
="value === max">
              +
            </button>
            <button type="button" tabindex="-1" (click)="decrement()" [disabled]="value === min">
              -
            </button>
          </div>
        </div>
      </div>
    </div>
  `
})
export class StockCounterComponent {
  @Input() step: number = 1;
  @Input() min: number = 0;
  @Input() max: number = 100;

  @Output() changed = new EventEmitter
 
<number>();

  value: number = 0;
  focused: boolean;

  increment() {
    if (this.value < this.max) {
      this.value = this.value + this.step;
      this.changed.emit(this.value);
    }
  }

  decrement() {
    if (this.value > this.min) {
      this.value = this.value - this.step;
      this.changed.emit(this.value);
    }
  }

  private onBlur(event: FocusEvent) {
    this.focused = false;
    event.preventDefault();
    event.stopPropagation();
  }

  private onKeyUp(event: KeyboardEvent) {
    let handlers = {
      ArrowDown: () => this.decrement(),
      ArrowUp: () => this.increment()
    };

    if (handlers[event.code]) {
      handlers[event.code]();
      event.preventDefault();
      event.stopPropagation();
    }
  }

  private onFocus(event: FocusEvent) {
    this.focused = true;
    event.preventDefault();
    event.stopPropagation();
  }

}

Test:

import { ComponentFixture, TestBed } from ‘@angular/core/testing‘;
import { BrowserDynamicTestingModule, platformBrowserDynamicTesting } from ‘@angular/platform-browser-dynamic/testing‘;
import { DebugElement } from ‘@angular/core‘;
import { StockCounterComponent } from ‘./stock-counter.component‘;
import { By } from ‘@angular/platform-browser‘;

TestBed.initTestEnvironment(
  BrowserDynamicTestingModule,
  platformBrowserDynamicTesting()
);

describe(‘StockCounterComponent‘, () => {

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

  beforeEach(() => {
    TestBed.configureTestingModule({
      declarations: [StockCounterComponent]
    });

    fixture = TestBed.createComponent(StockCounterComponent);
    component = fixture.componentInstance;
    el = fixture.debugElement;

    component.value = 0;
  });

  it(‘should increase the value when + button is clicked‘, () => {
    el.query(By.css(‘button:first-child‘)).triggerEventHandler(‘click‘, null);
    expect(component.value).toBe(1);
    el.query(By.css(‘button:first-child‘)).triggerEventHandler(‘click‘, null);
    fixture.detectChanges();
    expect(component.value).toBe(2);
    expect(el.query(By.css(‘p‘)).nativeElement.textContent).toBe(‘2‘);
  });

  it(‘should decrease the value when - button is clicked‘, () => {
    component.value = 2;
    fixture.detectChanges();
    el.query(By.css(‘button:last-child‘)).triggerEventHandler(‘click‘, null);
    fixture.detectChanges();
    expect(component.value).toBe(1);
    expect(el.query(By.css(‘p‘)).nativeElement.textContent).toBe(‘1‘);
  });

  it(‘should show the right value in p tag when the arrow up key is pressed‘, () => {
    const event = new Event(‘KeyboardEvent‘) as any;
    event.code = "ArrowUp";
    el.query(By.css(‘.stock-counter > div > div‘)).triggerEventHandler(‘keydown‘, event);
    fixture.detectChanges();
    expect(component.value).toBe(1);
    expect(el.query(By.css(‘p‘)).nativeElement.textContent).toBe(‘1‘);
  });
});

[Angular] Test component template