title: Passing an event object to enzyme .simulate
body: <p>I am using Jest and Enzyme to test a React checkbox component.</p>
  
  <p>This is my test:</p>
  
  <pre><code>it('triggers checkbox onChange event', () =&gt; {
    const configs = {
      default: true,
      label: 'My Label',
      element: 'myElement',
    }
    const checkbox = shallow(
      &lt;CheckBox
        configs={configs}
      /&gt;
    )
    checkbox.find('input').simulate('click')
  })
  </code></pre>
  
  <p>I get this error however when running the test:</p>
  
  <pre><code>TypeError: Cannot read property 'target' of undefined
  </code></pre>
  
  <p>This is the input for my component:</p>
  
  <pre><code>&lt;div className="toggle-btn sm"&gt;
    &lt;input 
      id={this.props.configs.element} 
      className="toggle-input round" 
      type="checkbox" 
      defaultChecked={ this.props.defaultChecked } 
      onClick={ e =&gt; this.onChange(e.target) }
    &gt;
    &lt;/input&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>I <em>think</em> that <a href="https://github.com/airbnb/enzyme/issues/592#issuecomment-246259252" rel="noreferrer">I need to pass an event as the second object to <code>simulate</code></a> but I am not sure how to do this.</p>
  
  <p>Thanks</p>