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."

it('can scryRenderedDOMComponentsWithClass with TextComponent', function() {
    var Wrapper = React.createClass({
      render: function() {
        return <div>Hello <span>Jim</span></div>;
      },
    });
    var renderedComponent = ReactTestUtils.renderIntoDocument(<Wrapper />);
    var scryResults = ReactTestUtils.scryRenderedDOMComponentsWithClass(
      renderedComponent,
      'NonExistentClass'
    );
    expect(scryResults.length).toBe(0);
  });
  it('can scryRenderedDOMComponentsWithClass with className contains \\n', function() {
    var Wrapper = React.createClass({
      render: function() {
        return <div>Hello <span className={'x\ny'}>Jim</span></div>;
      },
    });
    var renderedComponent = ReactTestUtils.renderIntoDocument(<Wrapper />);
    var scryResults = ReactTestUtils.scryRenderedDOMComponentsWithClass(
      renderedComponent,
      'x'
    );
    expect(scryResults.length).toBe(1);
  });
  it('can scryRenderedDOMComponentsWithClass with multiple classes', function() {
    var Wrapper = React.createClass({
      render: function() {
        return <div>Hello <span className={'x y z'}>Jim</span></div>;