在 firstUpdated 中对 LitElement 事件进行单元测试

Question

我有一个简单的混合：

export const mixin = superclass => class extends superclass {
  firstUpdated() {
    super.firstUpdated();
    this.dispatchEvent(new CustomEvent('my-event', {
      bubbles: true,
      composed: true,
      detail: {
        myEventTriggered: true,
      },
    }));
  }
};

我想测试 my-event 是否被触发。这是我的测试：

it('dispatches the custom event', async () => {
  const tag = class extends mixin(LitElement) {};
  const el = await fixture(`<${tag}></${tag}>`);
  setTimeout(() => el.firstUpdated());
  const { detail } = await oneEvent(el, 'my-event');
  expect(detail.myEventTriggered).to.be.true;
});

这按预期工作，但我不确定 setTimeout(() => el.firstUpdated()); 行。不应该在 await fixture 之后调用 firstUpdated 吗？我正在关注 open-wc's testing guide.

Answer 1

从@daKMor得到了答案：

testing firstUpdated is a little tricky as as soon as you add it to the dom it's executed (with an arbitrary delay depending on the work your element is doing) https://lit-element.polymer-project.org/guide/lifecycle#firstupdated

what you can do is:
it('dispatches a custom event on firstUpdated', async () => {
  const tag = class extends mixin(LitElement) {};
  const el = fixtureSync(`<${tag}></${tag}>`);
  const ev = await oneEvent(el, 'my-event');
  expect(ev).to.exist;
});

it('dispatches a custom event on connectedCallback', async () => {
  class Foo extends mixin(class {}) {};
  const el = new Foo();
  setTimeout(() => el.connectedCallback());
  const ev = await oneEvent(el, 'my-event');
  expect(ev).to.exist;
});
Note: this is untested code - if it works pls let me know and we could add that info and a little description to the faq. Maybe you could do a Pull Request?

对于connectedCallback，因为这个回调是在调用fixture之后立即触发的，所以你不能再捕捉到它了。您可以做的是定义一个新组件并在 setTimeout 中测试其回调函数。 HTMLElement 或 LitElement 是必需的，因为 oneEvent 向元素添加了一个事件侦听器。

it('dispatches a custom event on connectedCallback', () => {
  const tag = defineCE(class extends mixin(LitElement) {});
  const foo = document.createElement(`${tag}`);
  setTimeout(() => foo.connectedCallback());
  const ev = await oneEvent(foo, 'connected-callback');
  expect(ev).to.exist;
});

在 firstUpdated 中对 LitElement 事件进行单元测试

Unit testing LitElement events in firstUpdated

unit-testing

web-component

lit-element