Appears to be working in Firefox but at least Chrome & Safari are broken. Should be a really recent regression so very few possible changes to blame...

Easiest repo: the todo list on our homepage.

ReactDOM = require('ReactDOM');
    ReactDOMServer = require('ReactDOMServer');
  });
  describe('updateDOM', function() {
    var ReactTestUtils;
    beforeEach(function() {
      ReactTestUtils = require('ReactTestUtils');
    });
    it('should handle className', function() {
      var container = document.createElement('div');
      ReactDOM.render(<div style={{}} />, container);
      ReactDOM.render(<div className={'foo'} />, container);
      expect(container.firstChild.className).toEqual('foo');
      ReactDOM.render(<div className={'bar'} />, container);
      expect(container.firstChild.className).toEqual('bar');
      ReactDOM.render(<div className={null} />, container);
      expect(container.firstChild.className).toEqual('');
    });
    it('should gracefully handle various style value types', function() {
      var container = document.createElement('div');
      ReactDOM.render(<div style={{}} />, container);
      var stubStyle = container.firstChild.style;
      
      var setup = {display: 'block', left: '1px', top: 2, fontFamily: 'Arial'};
      ReactDOM.render(<div style={setup} />, container);
      expect(stubStyle.display).toEqual('block');
      expect(stubStyle.left).toEqual('1px');
      expect(stubStyle.fontFamily).toEqual('Arial');
      
      var reset = {display: '', left: null, top: false, fontFamily: true};