测试使用setInterval或setTimeout的Angular2组件

Question

我有一个相当典型的简单ng2组件,它调用服务来获取一些数据(轮播项目).它还使用setInterval每隔n秒在UI中自动切换轮播幻灯片.它运行得很好,但是当运行Jasmine测试时,我得到错误:"不能在异步测试区域内使用setInterval".

我尝试在this.zone.runOutsideAngular(()=> {...}中包装setInterval调用,但错误仍然存​​在.我认为改变测试以在fakeAsync区域中运行会解决问题,但后来我得到一个错误,说不允许在fakeAsync测试区内进行XHR调用(这确实有意义).

如何同时使用服务发出的XHR调用和间隔,同时仍能测试组件？我正在使用ng2 rc4,由angular-cli生成的项目.提前谢谢了.

我的组件代码:

constructor(private carouselService: CarouselService) {
}

ngOnInit() {
    this.carouselService.getItems().subscribe(items => { 
        this.items = items; 
    });
    this.interval = setInterval(() => { 
        this.forward();
    }, this.intervalMs);
}

而且来自Jasmine规范:

it('should display carousel items', async(() => {
    testComponentBuilder
        .overrideProviders(CarouselComponent, [provide(CarouselService, { useClass: CarouselServiceMock })])
        .createAsync(CarouselComponent).then((fixture: ComponentFixture<CarouselComponent>) => {
            fixture.detectChanges();
            let compiled = fixture.debugElement.nativeElement;
            // some expectations here;
    });
}));

Answer 1

清洁代码是可测试的代码.setInterval有时难以测试,因为时机永远不会完美.您应该将其抽象setTimeout为可以模拟测试的服务.在模拟中,您可以使用控件来处理间隔的每个刻度.例如

class IntervalService {
  interval;

  setInterval(time: number, callback: () => void) {
    this.interval = setInterval(callback, time);
  }

  clearInterval() {
    clearInterval(this.interval);
  }
}

class MockIntervalService {
  callback;

  clearInterval = jasmine.createSpy('clearInterval');

  setInterval(time: number, callback: () => void): any {
    this.callback = callback;
    return null;
  }

  tick() {
    this.callback();
  }
}

现在,MockIntervalService您可以控制每个滴答,这在测试期间更容易推理.还有一个间谍来检查clearInterval组件被销毁时是否调用该方法.

对于您CarouselService,因为它也是异步的,请看这篇文章以获得一个好的解决方案.

以下是使用前面提到的服务的完整示例(使用RC 6).

import { Component, OnInit, OnDestroy } from '@angular/core';
import { CommonModule } from '@angular/common';
import { TestBed } from '@angular/core/testing';

class IntervalService {
  interval;

  setInterval(time: number, callback: () => void) {
    this.interval = setInterval(callback, time);
  }

  clearInterval() {
    clearInterval(this.interval);
  }
}

class MockIntervalService {
  callback;

  clearInterval = jasmine.createSpy('clearInterval');

  setInterval(time: number, callback: () => void): any {
    this.callback = callback;
    return null;
  }

  tick() {
    this.callback();
  }
}

@Component({
  template: '<span *ngIf="value">{{ value }}</span>',
})
class TestComponent implements OnInit, OnDestroy {
  value;

  constructor(private _intervalService: IntervalService) {}

  ngOnInit() {
    let counter = 0;
    this._intervalService.setInterval(1000, () => {
      this.value = ++counter;
    });
  }

  ngOnDestroy() {
    this._intervalService.clearInterval();
  }
}

describe('component: TestComponent', () => {
  let mockIntervalService: MockIntervalService;

  beforeEach(() => {
    mockIntervalService = new MockIntervalService();
    TestBed.configureTestingModule({
      imports: [ CommonModule ],
      declarations: [ TestComponent ],
      providers: [
        { provide: IntervalService, useValue: mockIntervalService }
      ]
    });
  });

  it('should set the value on each tick', () => {
    let fixture = TestBed.createComponent(TestComponent);
    fixture.detectChanges();
    let el = fixture.debugElement.nativeElement;
    expect(el.querySelector('span')).toBeNull();

    mockIntervalService.tick();
    fixture.detectChanges();
    expect(el.innerHTML).toContain('1');

    mockIntervalService.tick();
    fixture.detectChanges();
    expect(el.innerHTML).toContain('2');
  });

  it('should clear the interval when component is destroyed', () => {
    let fixture = TestBed.createComponent(TestComponent);
    fixture.detectChanges();
    fixture.destroy();
    expect(mockIntervalService.clearInterval).toHaveBeenCalled();
  });
});