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."

) {
    ret = ret.concat(
      findAllInRenderedTreeInternal(inst._renderedComponent, test)
    );
  }
  return ret;
}
/**
 * Todo: Support the entire DOM.scry query syntax. For now, these simple
 * utilities will suffice for testing purposes.
 * @lends ReactTestUtils
 */
var ReactTestUtils = {
  renderIntoDocument: function(instance) {
    var div = document.createElement('div');
    
    
    
    
    
    return ReactDOM.render(instance, div);
  },
  isElement: function(element) {
    return ReactElement.isValidElement(element);
  },
  isElementOfType: function(inst, convenienceConstructor) {
    return (
      ReactElement.isValidElement(inst) &&
      inst.type === convenienceConstructor
    );