title: shallowMount behaves like mount when lazy loading a component
body: <p>I'm testing a Nuxt app with <code>vue-test-utils</code> (version 1.0.0-beta.29), and I'm lazy loading the <code>child</code> component. When testing, I want to <code>shallowMount</code> the <code>parent</code> component to stub the <code>child</code>s (I don't want to render the <code>child</code> component because of its dependencies).</p>
  
  <p>Instead of creating <code>child</code> stubs, the whole component tree is rendering in the <code>shallowMount</code>. If I load the components without lazy loading, <code>shallowMount</code> works as expected.</p>
  
  <p>It seems that the problem has already been faced and solved here: <a href="https://github.com/vuejs/vue-test-utils/issues/959" rel="nofollow noreferrer">https://github.com/vuejs/vue-test-utils/issues/959</a></p>
  
  <p>I've tried to pass <code>{ shouldProxy: true }</code> as a mounting option, or stubbing manually the component by passing <code>{ stubs: ['componentname'] }</code>, but the problem is still happening.</p>
  
  <p><code>parent</code> component:</p>
  
  <pre><code>&lt;template&gt;
    &lt;div id="wrapper"&gt;
      &lt;div 
        v-for="item in markets"
        class="item-wrapper"&gt;
        &lt;Child :market="item"/&gt;
      &lt;/div&gt;
    &lt;/div&gt;
  &lt;/template&gt;
  
  &lt;script&gt;
  export default {
    components: {
      Child: () =&gt; import('./TimelineItem.vue')
    },
    props: {
      markets: {
        type: Array,
        default: () =&gt; []
      }
    }
  }
  &lt;/script&gt;
  </code></pre>
  
  <p><code>child</code> component:</p>
  
  <pre><code>&lt;template&gt;
    &lt;div&gt;
      Child
    &lt;/div&gt;
  &lt;/template&gt;
  
  &lt;script&gt;
  
  export default {
    props: {
      market: {
        type: Object,
        default: () =&gt; {}
      }
    }
  }
  &lt;/script&gt;
  </code></pre>
  
  <p>Snapshot:</p>
  
  <pre class="lang-html prettyprint-override"><code>&lt;div id="wrapper"&gt;
    &lt;div class="item-wrapper"&gt;
      &lt;div&gt;Child&lt;/div&gt;
    &lt;/div&gt;
    &lt;div class="item-wrapper"&gt;
      &lt;div&gt;Child&lt;/div&gt;
    &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>I expected to have an snapshot like this:</p>
  
  <pre class="lang-html prettyprint-override"><code>&lt;div id="wrapper"&gt;
    &lt;div class="item-wrapper"&gt;
      &lt;child-stub&gt;&lt;/child-stub&gt;
    &lt;/div&gt;
    &lt;div class="item-wrapper"&gt;
      &lt;child-stub&gt;&lt;/child-stub&gt;
    &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>