在jasmine beforeEach里修改UI元素的一个side effect

import { Component } from '@angular/core';
import { async, ComponentFixture, TestBed } from '@angular/core/testing';
import { ReactiveFormsModule } from '@angular/forms';
import { ActivatedRoute } from '@angular/router';
import {
  CheckoutDeliveryService,
  DeliveryMode,
  I18nTestingModule,
} from '@spartacus/core';
import { Observable, of } from 'rxjs';
import { CheckoutConfigService } from '../../services/checkout-config.service';
import { CheckoutStepService } from '../../services/checkout-step.service';
import { DeliveryModeComponent } from './delivery-mode.component';
import createSpy = jasmine.createSpy;
import { LoaderState } from '../../../../../../core/src/state/utils/loader';
import { By } from '@angular/platform-browser';

@Component({
  selector: 'cx-spinner',
  template: '',
})
class MockSpinnerComponent {}

class MockCheckoutDeliveryService {
  loadSupportedDeliveryModes = createSpy();
  setDeliveryMode = createSpy();
  getSupportedDeliveryModes(): Observable<DeliveryMode[]> {
    return of();
  }
  getSelectedDeliveryMode(): Observable<DeliveryMode> {
    return of();
  }
  getLoadSupportedDeliveryModeProcess(): Observable<LoaderState<void>> {
    return of();
  }
}

class MockCheckoutConfigService {
  getPreferredDeliveryMode(): string {
    return '';
  }
}

class MockCheckoutStepService {
  next = createSpy();
  back = createSpy();
  getBackBntText(): string {
    return 'common.back';
  }
}

const mockActivatedRoute = {
  snapshot: {
    url: ['checkout', 'delivery-mode'],
  },
};

describe('DeliveryModeComponent', () => {
  let component: DeliveryModeComponent;
  let fixture: ComponentFixture<DeliveryModeComponent>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [ReactiveFormsModule, I18nTestingModule],
      declarations: [DeliveryModeComponent, MockSpinnerComponent],
      providers: [
        {
          provide: CheckoutDeliveryService,
          useClass: MockCheckoutDeliveryService,
        },
        { provide: CheckoutStepService, useClass: MockCheckoutStepService },
        { provide: CheckoutConfigService, useClass: MockCheckoutConfigService },
        { provide: ActivatedRoute, useValue: mockActivatedRoute },
      ],
    }).compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(DeliveryModeComponent);
    component = fixture.componentInstance;
    console.log('beforeEach outside continue button describe');
  });

  describe('continue button', () =>{

    const getContinueBtn = () => fixture.debugElement.query(By.css('.cx-checkout-btns .btn-primary'));
    const setDeliveryModeId = (value: string) =>  
      component.mode.controls['deliveryModeId'].setValue(value);

    beforeEach(() => {
      setDeliveryModeId('aa');
      fixture.detectChanges();

      let button = getContinueBtn();
      console.log('beforeEach inside continue button describe, component.deliveryModeInvalid: ' + 
      component.deliveryModeInvalid + ' button.disabled: ' + button.nativeElement.disabled );

      setDeliveryModeId(null);
      fixture.detectChanges();

      console.log('set delivery mode id to null!');
      button = getContinueBtn();
      console.log('after that, component.deliveryModeInvalid: ' + 
      component.deliveryModeInvalid + ' button.disabled: ' + button.nativeElement.disabled );
    });
      
    it('should be available', () => {
      const button = getContinueBtn();
      console.log('fixture.detectChanges is put in beforeEach: ' + button);
      //fixture.detectChanges();
      //button = getContinueBtn();
      //console.log('after call fixture.detectChanges: ' + button);
      expect(button).toBeTruthy();
    });

    /*it('should be disabled when delivery mode is not selected', () => {
      setDeliveryModeId(null);
      fixture.detectChanges();
      expect(getContinueBtn().nativeElement.disabled).toBe(true);
    });*/
  });
});