<p dir="auto"><strong>Do you want to request a <em>feature</em> or report a <em>bug</em>?</strong></p>
<p dir="auto">Bug</p>
<p dir="auto"><strong>What is the current behavior?</strong></p>
<p dir="auto">Let's say we have a component that recieve an array and renders them in a list</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="var List = React.createClass({
  render: function() {
    return (
    &lt;div&gt;
        {
        this.props.items.map(function(item){
            return &lt;div className=&quot;item&quot; key={item.id}&gt;{item.name}&lt;/div&gt;;
        })
      }
     &lt;/div&gt;
    )
  }
});"><pre class="notranslate"><code class="notranslate">var List = React.createClass({
  render: function() {
    return (
    &lt;div&gt;
        {
        this.props.items.map(function(item){
            return &lt;div className="item" key={item.id}&gt;{item.name}&lt;/div&gt;;
        })
      }
     &lt;/div&gt;
    )
  }
});
</code></pre></div>
<p dir="auto">and let's say we passed the following array:</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="var items = [{id:'1', name: 'one'},{id:'1', name: 'two'}];"><pre class="notranslate"><code class="notranslate">var items = [{id:'1', name: 'one'},{id:'1', name: 'two'}];
</code></pre></div>
<p dir="auto">since the id is a duplicate, React will render only one item and throws the following warning</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="Encountered two children with the same key, `1`. Child keys must be unique; when two children share a key, only the first child will be used.
    in div (created by List)
    in List"><pre class="notranslate"><code class="notranslate">Encountered two children with the same key, `1`. Child keys must be unique; when two children share a key, only the first child will be used.
    in div (created by List)
    in List
</code></pre></div>
<p dir="auto">Here is a demo for the above <a href="https://jsfiddle.net/69z2wepo/55187/" rel="nofollow">https://jsfiddle.net/69z2wepo/55187/</a></p>
<p dir="auto">However, when using ReactTestUtils to shallow render the list, it returns 2 items instead of 1.</p>
<p dir="auto">Below a testcase for demonstration purpose:</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="describe('&lt;List&gt;', () =&gt;

it('should render the correct number of items', () =&gt; {

    let items = [{id:'1', name: 'one'},{id:'1', name: 'two'}];
    let renderer = ReactTestUtils.createRenderer();
    let result= renderer.render(&lt;List items={items} /&gt;);

    // the following testcase should fail
    expect(result.props.children.length).toBe(2)

}))"><pre class="notranslate"><code class="notranslate">describe('&lt;List&gt;', () =&gt;

it('should render the correct number of items', () =&gt; {

    let items = [{id:'1', name: 'one'},{id:'1', name: 'two'}];
    let renderer = ReactTestUtils.createRenderer();
    let result= renderer.render(&lt;List items={items} /&gt;);

    // the following testcase should fail
    expect(result.props.children.length).toBe(2)

}))
</code></pre></div>
<p dir="auto">**If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem</p>
<p dir="auto">See above</p>
<p dir="auto"><strong>What is the expected behavior?</strong></p>
<p dir="auto">Shallow Renderer should behave like in the browser, in this case it should return 1 children instead of 2.</p>
<p dir="auto"><strong>Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?</strong></p>
<p dir="auto">15.0.0</p>
<p dir="auto"><strong>Do you want to request a <em>feature</em> or report a <em>bug</em>?</strong></p>
<p dir="auto">Bug - regression</p>
<p dir="auto"><strong>What is the current behavior?</strong></p>
<p dir="auto">In react 16 when creating a <code class="notranslate">&lt;select size="3"&gt;</code> (size &gt; 1) the first child  is automatically getting marked as selected. In React 16 there does not seem to be a way to specify no  gets selected by default</p>
<p dir="auto"><a href="https://codesandbox.io/s/m76ozkwm89" rel="nofollow">https://codesandbox.io/s/m76ozkwm89</a></p>
<p dir="auto"><strong>What is the expected behavior?</strong></p>
<p dir="auto">In React 15 unless you marked an option to be selected  no options were selected by default.</p>
<p dir="auto"><a href="https://codesandbox.io/s/6894m3k9w" rel="nofollow">https://codesandbox.io/s/6894m3k9w</a></p>
<p dir="auto"><strong>Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?</strong></p>
<p dir="auto">Reproducible in Chrome 72 and Firefox 59.</p>
<p dir="auto"><strong>Note:</strong> this is almost a duplicate of <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="295990671" data-permission-text="Title is private" data-url="https://github.com/facebook/react/issues/12200" data-hovercard-type="issue" data-hovercard-url="/facebook/react/issues/12200/hovercard" href="https://github.com/facebook/react/issues/12200">#12200</a>. In fact, I copied issue text and codesandbox examples, just changing <code class="notranslate">multiple</code> to <code class="notranslate">size="3"</code>.</p>