To reproduce, open http://jsfiddle.net/0jjnaghw/
Error is logged to browser dev tools (in Chrome & Firefox, somehow not in Safari).

Happens on v15.0.0-rc.2 and on latest master version.

The assignment of additional event data to the newly created SyntheticEvent triggers a console error:
https://github.com/facebook/react/blob/3a4e1dbb5b2957875cab6af11a5e5934e125a0d8/src/test/ReactTestUtils.js#L502

> "Warning: This synthetic event is reused for performance reasons."

);
      },
    });
    var handler = jasmine.createSpy('spy');
    var shallowRenderer = ReactTestUtils.createRenderer();
    var result = shallowRenderer.render(<SomeComponent handleClick={handler} />);
    expect(() => ReactTestUtils.Simulate.click(result)).toThrow(
      'TestUtils.Simulate expects a component instance and not a ReactElement.' +
      'TestUtils.Simulate will not work if you are using shallow rendering.'
    );
    expect(handler).not.toHaveBeenCalled();
  });
  it('can scry with stateless components involved', function() {
    var Stateless = () => <div><hr /></div>;
    var SomeComponent = React.createClass({
      render: function() {
        return (
          <div>
            <Stateless />
            <hr />
          </div>
        );
      },
    });
    var inst = ReactTestUtils.renderIntoDocument(<SomeComponent />);
    var hrs = ReactTestUtils.scryRenderedDOMComponentsWithTag(inst, 'hr');
    expect(hrs.length).toBe(2);
  });
});