title: Find element with Enzyme in nested React component
body: <p>I am trying to write a for my component <code>TestComponent</code> that ensures the callback is fired when the user clicks on a button.  However, the button is not found (though I can see it in the HTML by calling <code>console.log(wrapper.html())</code>.</p>
  
  <p>The button is inside another component that is used within <code>TestComponent</code>, if that matters.</p>
  
  <p>Here is my test:</p>
  
  <pre><code>import React from 'react';
  import expect from 'expect';
  import { shallow } from 'enzyme';
  import sinon from 'sinon';
  import TestComponent from './test-component.jsx';
  
  describe('&lt;TestComponent/&gt;', () =&gt; {
    it('clicking "continue" button fires the callback', () =&gt; {
      const onClickContinue = sinon.spy();
      const wrapper = shallow(&lt;TestComponent /&gt;);
      console.log(wrapper.find('.btn-primary').length); // 0
      console.log(wrapper.html());                      // does have `.btn-primary`
  
      // wrapper.find('.btn-primary').simulate('click');
      // expect(onClickContinue.calledOnce).toBe(true);
    });
  });
  </code></pre>
  
  <p>What am I doing wrong?  Thank you.</p>