<p dir="auto">If you add multiple child elements to a ToolTip, you will receive the following error:</p>
<p dir="auto"><strong>Invariant Violation</strong><br>
Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it's defined in.</p>

<ul class="contains-task-list">
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have searched the <a href="https://github.com/mui-org/material-ui/issues">issues</a> of this repository and believe that this is not a duplicate.</li>
</ul>
<h2 dir="auto">Expected Behavior</h2>
<p dir="auto">The current error message is associated with forgetting to import a component, making troubleshooting more difficult.</p>
<h2 dir="auto">Current Behavior</h2>
<p dir="auto">Either update the ToolTip component to allow multiple children, or throw a more descriptive error.</p>
<h2 dir="auto">Steps to Reproduce (for bugs)</h2>
<p dir="auto"><a href="https://codesandbox.io/s/qv37l9w609" rel="nofollow">https://codesandbox.io/s/qv37l9w609</a></p>
<h2 dir="auto">Context</h2>
<p dir="auto">Took extra time to find the cause of the Invariant Violation</p>
<h2 dir="auto">Your Environment</h2>

<table role="table">
<thead>
<tr>
<th>Tech</th>
<th>Version</th>
</tr>
</thead>
<tbody>
<tr>
<td>Material-UI</td>
<td>24</td>
</tr>
<tr>
<td>React</td>
<td>16</td>
</tr>
<tr>
<td>browser</td>
<td>Chrome</td>
</tr>
<tr>
<td>etc</td>
<td></td>
</tr>
</tbody>
</table>
<p dir="auto">Hi, for the url here: <a href="https://github.com/callemall/material-ui/blob/v1-beta/docs/src/pages/guides/testing.md#examples">Testing Documentation of material UI</a> where is 'material-ui/test-utils' coming from? is that a package included or does that need to be installed separately?</p>
<p dir="auto">Also, what is the best way to test your components when mounting them with Enzyme? there seem to be different suggestions which are adding to my confusion. 1. Pass context to the mount call: <code class="notranslate">const wrapper = mount( &lt;CreateAssessment  /&gt;, { context: {muiTheme}, childContextTypes: {muiTheme: React.PropTypes.object} } )</code></p>
<p dir="auto">or use Material-UI's mount wrapper?</p>


<ul dir="auto">
<li>[x ] I have searched the <a href="https://github.com/callemall/material-ui/issues">issues</a> of this repository and believe that this is not a duplicate.</li>
</ul>
<h2 dir="auto">Expected Behavior</h2>

<h2 dir="auto">Current Behavior</h2>

<h2 dir="auto">Steps to Reproduce (for bugs)</h2>

<ol dir="auto">
<li></li>
<li></li>
<li></li>
<li></li>
</ol>
<h2 dir="auto">Context</h2>
    
<h2 dir="auto">Your Environment</h2>

<table role="table">
<thead>
<tr>
<th>Tech</th>
<th>Version</th>
</tr>
</thead>
<tbody>
<tr>
<td>Material-UI</td>
<td>0.16.7</td>
</tr>
<tr>
<td>React</td>
<td>15.3.2</td>
</tr>
<tr>
<td>browser</td>
<td></td>
</tr>
<tr>
<td>Jest</td>
<td>21.2.1</td>
</tr>
<tr>
<td>Enzyme</td>
<td>3.1.1</td>
</tr>
<tr>
<td>etc</td>
<td></td>
</tr>
</tbody>
</table>