title: enzyme simulate 'click' doesn't work when it should
body: <p>I'm using Jest and Enzyme to test out a Form component, and I'm having trouble getting the click simulation to work. For reference: <code>Button</code> is a styled rebass Button, and exists in the form like this:  </p>
  
  <pre><code>&lt;Button
    type="reset"
    disabled={pristine || submitting}
    onClick={() =&gt; onClose(dirty)}
  &gt;
  </code></pre>
  
  <p>Here's the test that's failing:</p>
  
  <pre><code> it('should handle the onClose event', () =&gt; {
        const onCloseSpy = jest.fn();
        const renderedComponent = mount(renderFormUtil({ onClose: onCloseSpy }));
        expect(onCloseSpy).not.toHaveBeenCalled();
        console.log(renderedComponent.find(Form).props().onClose);
        renderedComponent
        .find(Button)
        .first()
        .simulate('click');
      expect(onCloseSpy).toHaveBeenCalled();
    });
  </code></pre>
  
  <p>What should be noted here, is that if I replace the simulate line with the following:  </p>
  
  <pre><code>renderedComponent
    .find(Button)
    .first()
    .props()
    .onClick();
  </code></pre>
  
  <p>then suddenly my test passes. How is this possible? If the onClick prop is correct, then doesn't that mean the click event is not calling the prop correctly?</p>