使用 CustomEvent 对dispatchEvent 进行玩笑测试

Question

我在尝试测试某个 CustomEvent 是否已在类中调度时收到误报。我正在用来jest.spyOn测试通过调用传递的特定 CustomEvent dispatchEvent。这是调度自定义事件的函数：

someFunction() {
    this.dispatchEvent(
        new CustomEvent('myEvent', {
            bubbles: true,
            composed: true,
            detail: { someProperty: this.localProperty },
        })
    );
}

测试尝试以这种方式验证预期事件：

let container;

beforeEach(() => {
    container = new SomeClass();
});


it('dispatches correct CustomEvent when someFunction is called', () => {
    const dispatchEventSpy = jest.spyOn(container, 'dispatchEvent');
    container.localProperty = '123';
    const customEvent = new CustomEvent('myEvent', {
        bubbles: true,
        composed: true,
        detail: { someProperty: 'wrong value' },
    });
    container.someFunction();
    // TODO: I expect the below to fail because the format passed in the custom event does not match the format in the container.
    expect(dispatchEventSpy).toHaveBeenCalledWith(customEvent);
    // If I use toBe instead and check the argument passed to dispatchEvent this way it fails even when they are the same. So I either get a false positive or a false negative.
    expect(dispatchEventSpy.mock.calls[0][0]).toBe(customEvent);
});

Answer 1

如果您在 jest 单元测试中记录此对象，您将看到结果非常相似：

console.log(new CustomEvent("myEvent", {
   bubbles: true,
   composed: true,
   detail: { someProperty: "123" },
}));
console.log(new CustomEvent("myEvent", {
  bubbles: true,
  composed: true,
  detail: { someProperty: "error" },
}));

就我而言，两者的结果都是： { isTrusted: [Getter] }

这就是为什么这不会失败的原因：

expect(dispatchEventSpy).toHaveBeenCalledWith(customEvent);

您可以使用dispatchEventSpy.mock.calls[0][0]访问预期对象以获得更好的断言：

  expect(dispatchEventSpy.mock.calls[0][0].detail).toEqual({
    someProperty: "123",
  });
  expect(dispatchEventSpy.mock.calls[0][0].bubbles).toEqual(true);
  expect(dispatchEventSpy.mock.calls[0][0].composed).toEqual(true);