title: has no method 'mountComponentIntoNode' with Jest + React
body: <p>Im brand new to React as well as Jest and I thought I had a fairly simple component but I keep getting this error and I dont see any info on it in their issues on GitHub and only one React specific, not Jest, question here. Full error is: <code>TypeError: Object &lt;UserInfo /&gt; has no method 'mountComponentIntoNode'</code></p>
  
  <p>React Code</p>
  
  <pre><code>/** @jsx React.DOM */
  var React = require('react');
  var Router = require('react-nested-router');
  
  var user = require('../lib/stores/user');
  
  /**
   * UserInfo
   *
   * Form for user's personal information.
  **/
  var UserInfo = React.createClass({
    handleSubmit: function(event) {
      event.preventDefault();
  
      user.firstName = this.refs.firstName.getDOMNode().value;
      user.lastName = this.refs.lastName.getDOMNode().value;
      user.dateOfBirth = this.refs.dob.getDOMNode().value;
      user.ssn = this.refs.ssn.getDOMNode().value;
  
      Router.transitionTo('/contact-info');
    },
  
    render: function() {
      return (
        &lt;section&gt;
          &lt;form onSubmit={this.handleSubmit}&gt;
            &lt;label class="first-name-label" htmlFor="first-name"&gt;First Name&lt;/label&gt;
            ... lots of inputs and labels ...
          &lt;/form&gt;
        &lt;/section&gt;
      );
    }
  });
  
  module.exports = UserInfo;
  </code></pre>
  
  <p>Jest Code</p>
  
  <pre><code>/** @jsx React.DOM */
  jest.dontMock('../application/views/user-info.jsx');
  var React = require('react/addons');
  var UserInfo = require('../application/views/user-info.jsx');
  var TestUtils = React.addons.TestUtils;
  
  describe('UserInfo', function () {
    it('example test only', function () {
      var userinfo = '&lt;UserInfo /&gt;'
      TestUtils.renderIntoDocument(userinfo);
    });
  });
  </code></pre>