title: How to test that a custom event from was fired from child component
body: <p>I've a <code>Vue</code> component with the following structure</p>
  
  <pre><code>// parent-component.vue
  &lt;main&gt;
    &lt;component :is="my.component" @custom-event="callback"/&gt;
  &lt;/main&gt;
  </code></pre>
  
  <p>The child component has always have the following <code>mixin</code></p>
  
  <pre><code>// child-shared-mixin.js
  export default {
    mounted() {
      this.$emit('custom-event')
    },
  }
  </code></pre>
  
  <p>Here is the example of the child component</p>
  
  <pre><code>// child-component.vue
  &lt;script&gt;
    import { ChildSharedMixin } from 'mixins'
  
    export default {
      mixins: [
        ChildSharedMixin
      ],
    }
  &lt;/script&gt;
  </code></pre>
  
  <p>So, whenever the <code>child</code> is mounted I trigger a event to the parent and then execute a callback.</p>
  
  <p>With <code>Jest</code> and <code>Vue Test Utils</code> how can I test that <code>mixin</code> has fired the <code>custom-event</code>?</p>