`SyntheticEvent.type` is undefined when received by the handler. Or the nativeEvent type for that matter.

Needs to be added in here somewhere: https://github.com/facebook/react/blob/3a4e1dbb5b2957875cab6af11a5e5934e125a0d8/src/test/ReactTestUtils.js#L496

I realize that it's not sustainable to have to set _all_ the possible fields for a simulated event, but the type at least makes sense for verification that you're getting the right _sort_ of event.

}
    return all[0];
  },
  /**
   * Pass a mocked component module to this method to augment it with
   * useful methods that allow it to be used as a dummy React component.
   * Instead of rendering as usual, the component will become a simple
   * <div> containing any provided children.
   *
   * @param {object} module the mock function object exported from a
   *                        module that defines the component to be mocked
   * @param {?string} mockTagName optional dummy root tag name to return
   *                              from render method (overrides
   *                              module.mockTagName if provided)
   * @return {object} the ReactTestUtils object (for chaining)
   */
  mockComponent: function(module, mockTagName) {
    mockTagName = mockTagName || module.mockTagName || 'div';
    module.prototype.render.mockImplementation(function() {
      return React.createElement(
        mockTagName,
        null,
        this.props.children
      );
    });
    return this;
  },
  /**
   * Simulates a top level event being dispatched from a raw event that occurred
   * on an `Element` node.