如何在 angular2 单元测试中更改 select 框的值？

Question

我有一个 Angular2 组件，其中包含一个 select 框，看起来像

<select [(ngModel)]="envFilter" class="form-control" name="envSelector" (ngModelChange)="onChangeFilter($event)">
    <option *ngFor="let env of envs" [ngValue]="env">{{env}}</option>
</select>

我正在尝试为 ngModelChange 事件编写单元测试。这是我最近一次失败的尝试

it("should filter and show correct items", async(() => {
    fixture.detectChanges();
    fixture.whenStable().then(() => {
        el = fixture.debugElement.query(By.name("envSelector"));
        fixture.detectChanges();
        makeResponse([hist2, longhist]);
        comp.envFilter = 'env3';
        el.triggerEventHandler('change', {});
        fixture.whenStable().then(() => {
            fixture.detectChanges();
            expect(comp.displayedHistory).toEqual(longhist);
        });
    });

我遇到麻烦的部分是更改基础模型的值 comp.envFilter = 'env3'; 不会触发 change 方法。我添加了 el.triggerEventHandler('change', {}); 但这抛出 Failed: Uncaught (in promise): ReferenceError: By is not defined。我在文档中找不到任何提示...有什么想法吗？

Answer 1

就错误而言。看来您只需要导入 By。这不是全球性的。它应该从以下模块导入

import { By } from '@angular/platform-browser';

就测试部分而言，这是我能够弄清楚的。当您更改组件中的值时，您需要触发更改检测以更新视图。您使用 fixture.detectChanges() 执行此操作。完成此操作后，通常应使用该值更新视图。

从测试类似于您的示例的内容来看，情况似乎并非如此。似乎在更改检测之后仍有一些异步任务正在进行。假设我们有以下

const comp = fixture.componentInstance;
const select = fixture.debugElement.query(By.css('select'));

comp.selectedValue = 'a value';
fixture.DetectChanges();
expect(select.nativeElement.value).toEqual('1: a value');

这似乎不起作用。似乎有一些异步正在进行，导致尚未设置该值。所以我们需要通过调用 fixture.whenStable

来等待异步任务

comp.selectedValue = 'a value';
fixture.DetectChanges();
fixture.whenStable().then(() => {
  expect(select.nativeElement.value).toEqual('1: a value');
});

以上方法可行。但现在我们需要触发更改事件，因为它不会自动发生。

fixture.whenStable().then(() => {
  expect(select.nativeElement.value).toEqual('1: a value');

  dispatchEvent(select.nativeElement, 'change');
  fixture.detectChanges();
  fixture.whenStable().then(() => {
    // component expectations here
  });
});

现在我们有另一个来自事件的异步任务。所以我们需要再次稳定它

下面是我测试过的完整测试。它是 source code integration tests 示例的重构。他们使用 fakeAsync 和 tick，这类似于使用 async 和 whenStable。但是对于 fakeAsync，你不能使用 templateUrl，所以我认为最好将其重构为使用 async。

源代码测试也进行了一种双重单向测试，首先测试要查看的模型，然后要测试要查看的模型。虽然看起来您的测试正在尝试进行某种双向测试，从模型到模型。所以我对其进行了一些重构以更好地适应您的示例。

import { Component } from '@angular/core';
import { TestBed, getTestBed, async } from '@angular/core/testing';
import { FormsModule } from '@angular/forms';
import { By } from '@angular/platform-browser';
import { dispatchEvent } from '@angular/platform-browser/testing/browser_util';

@Component({
  selector: 'ng-model-select-form',
  template: `
    <select [(ngModel)]="selectedCity" (ngModelChange)="onSelected($event)">
      <option *ngFor="let c of cities" [ngValue]="c"> {{c.name}} </option>
    </select>
  `
})
class NgModelSelectForm {
  selectedCity: {[k: string]: string} = {};
  cities: any[] = [];

  onSelected(value) {
  }
}

describe('component: NgModelSelectForm', () => {
  beforeEach(() => {
    TestBed.configureTestingModule({
      imports: [ FormsModule ],
      declarations: [ NgModelSelectForm ]
    });
  });

  it('should go from model to change event', async(() => {
    const fixture = TestBed.createComponent(NgModelSelectForm);
    const comp = fixture.componentInstance;
    spyOn(comp, 'onSelected');
    comp.cities = [{'name': 'SF'}, {'name': 'NYC'}, {'name': 'Buffalo'}];
    comp.selectedCity = comp.cities[1];
    fixture.detectChanges();
    const select = fixture.debugElement.query(By.css('select'));

    fixture.whenStable().then(() => {
      dispatchEvent(select.nativeElement, 'change');
      fixture.detectChanges();
      fixture.whenStable().then(() => {
        expect(comp.onSelected).toHaveBeenCalledWith({name : 'NYC'});
        console.log('after expect NYC');
      });
    });
  }));
});

Answer 2

看这个例子，来自 angular 来源 (template_integration_spec.ts)

@Component({
  selector: 'ng-model-select-form',
  template: `
    <select [(ngModel)]="selectedCity">
      <option *ngFor="let c of cities" [ngValue]="c"> {{c.name}} </option>
    </select>
  `
})
class NgModelSelectForm {
  selectedCity: {[k: string]: string} = {};
  cities: any[] = [];
}



  it('with option values that are objects', fakeAsync(() => {
       const fixture = TestBed.createComponent(NgModelSelectForm);
       const comp = fixture.componentInstance;
       comp.cities = [{'name': 'SF'}, {'name': 'NYC'}, {'name': 'Buffalo'}];
       comp.selectedCity = comp.cities[1];
       fixture.detectChanges();
       tick();

       const select = fixture.debugElement.query(By.css('select'));
       const nycOption = fixture.debugElement.queryAll(By.css('option'))[1];

       // model -> view
       expect(select.nativeElement.value).toEqual('1: Object');
       expect(nycOption.nativeElement.selected).toBe(true);

       select.nativeElement.value = '2: Object';
       dispatchEvent(select.nativeElement, 'change');
       fixture.detectChanges();
       tick();

       // view -> model
       expect(comp.selectedCity['name']).toEqual('Buffalo');
     }));

Answer 3

我发现 peeskillet 的回答非常有用，但遗憾的是它有点过时了，因为发送事件的方式已经改变。我还发现对 whenStable() 进行了不必要的调用。所以这是使用 peeskillet 设置的更新测试：

    it('should go from model to change event', async(() => {
        const fixture = TestBed.createComponent(NgModelSelectForm);
        const comp = fixture.componentInstance;
        spyOn(comp, 'onSelected');
        comp.cities = [{'name': 'SF'}, {'name': 'NYC'}, {'name': 'Buffalo'}];
        comp.selectedCity = comp.cities[1];
        fixture.detectChanges();
        const select = fixture.debugElement.query(By.css('select'));

        fixture.whenStable().then(() => {
            select.nativeElement.dispatchEvent(new Event('change'));
            fixture.detectChanges();
            expect(comp.onSelected).toHaveBeenCalledWith({name : 'NYC'});
            console.log('after expect NYC');
        });
    }));

Answer 4

希望这会对某人有所帮助。与 OP 提出的问题相同，但代码略有不同。

在 Angular 7.

中工作

HTML:

<select id="dashboard-filter" class="form-control" name="dashboard-filter" [ngModel]="dashboardFilterValue" (ngModelChange)="onFilterChange($event)"
              [disabled]="disabled">
  <option *ngFor="let filter of dashboardFilters" [ngValue]="filter.value">{{ filter.name }}</option>
</select>

单元测试：

it('onFilterChange', () => {

  // ensure dropdown is enabled
  expect(component.disabled).toBe(false)

  // spies
  spyOn(component, 'onFilterChange').and.callThrough()
  spyOn(component.filterChange, 'emit')

  // initially the 3rd item in the dropdown is selected
  const INITIAL_FILTER_INDEX = 2
  // we want to select the 5th item in the dropdown
  const FILTER_INDEX = 4
  // the expected filter value is the value of the 5th dashboard filter (as used to populate the dropdown)
  const EXPECTED_FILTER_VALUE = getDashboardFiltersData.dashboardFilters[FILTER_INDEX].value

  // handle on the dropdown
  const filterDropdown = fixture.debugElement.query(By.css('select')).nativeElement

  // let bindings complete
  fixture.whenStable().then(() => {

    // ensure filterDropdown.value is stable
    expect(filterDropdown.value).toContain(getDashboardFiltersData.dashboardFilters[INITIAL_FILTER_INDEX].value)

    // update filterDropdown.value and dispatch change event
    filterDropdown.value = filterDropdown.options[FILTER_INDEX].value
    filterDropdown.dispatchEvent(new Event('change'))

    // check component data
    expect(component.dashboardFilterValue).toBe(EXPECTED_FILTER_VALUE)
    expect(component.dashboardFilterChangeInProgress).toBe(false)

    // check spies
    expect(component.onFilterChange).toHaveBeenCalledWith(EXPECTED_FILTER_VALUE)
    expect(setDashboardFilterSpy).toHaveBeenCalledWith(EXPECTED_FILTER_VALUE)
    expect(component.filterChange.emit).toHaveBeenCalledWith(true)
  })
})

如何在 angular2 单元测试中更改 select 框的值？

How to change value of a select box in angular2 unit test?

unit-testing

angular

typescript

karma-jasmine

angular2-testing