如何从测试代码触发Angular Material MatSelect上的selectionChange事件

问题描述

我有一个嵌入Angular Material MatSelect元素的Component.

I have a Component which embeds an Angular Material MatSelect element.

在我正在编写的测试中，我需要模拟对某个选项的选择，并确保与该MatSelect元素关联的selectionChange Observable实际上触发.

In a test that I am writing, I need to simulate the selection of a certain option and make sure that the selectionChange Observable associated to that MatSelect element actually fires.

到目前为止，我的代码是

So far my code is

const mySelect: MatSelect = fixture.nativeElement.querySelector('#mySelect');
mySelect.value = 'new value';

但是不幸的是，这并没有使mySelect.selectionChange通知，因此无法进行我的测试.关于如何执行此操作的任何想法都非常欢迎.

But unfortunately this is not making the mySelect.selectionChange notify, and therefore my test work. Any idea on how this could be performed is very welcome.

推荐答案

我只需通过@ViewChild访问要测试的组件中的MatSelect，以便您可以轻松地在单元测试中使用它.

I would simply access the MatSelect in the component you want to test via @ViewChild so you can easily use it in your unit test.

/** For testing purposes */
@ViewChild(MatSelect) public matSelect: MatSelect;

在测试中，我将通过_selectViaInteraction()选择所需的选项，这模拟了该选项已由用户选择.

And in your test I would select the desired option via _selectViaInteraction(), this simulates that the option was selected by the user.

it('test selectionChange', () => {    
  // make sure the mat-select has the expected mat-options
  const options: MatOption[] = component.matSelect.options.toArray();
  expect(options.length).toBe(3);
  expect(options[0].viewValue).toBe('Steak');
  expect(options[1].viewValue).toBe('Pizza');
  expect(options[2].viewValue).toBe('Tacos');

  // set up a spy on the function that will be invoked via selectionChange
  const spy = spyOn(component, 'onChange').and.callThrough();
  expect(spy).not.toHaveBeenCalled();

  // select the option
  options[1]._selectViaInteraction();
  fixture.detectChanges();

  // selectionChange was called and the option is now selected    
  expect(spy).toHaveBeenCalledTimes(1);
  expect(options[1].selected).toBe(true);
});

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