Hover states with Selenium 2..

We do a lot of automated tests on Selenium 2, and recently we noticed that some of our tests that attempt to verify mouseover/hover states intermittently break. We could see the mouseover event get fired, but then suddenly it would stop.

The phenomenon at first made us suspect there were possible race conditions in our JavaScript code. Were we accidentally clearing/hiding elements before WebDriver could reach them? Was the web browser loading multiple times and clearing out the original state? Or was it an issue in Selenium 2, since it attempts to calculate the center position of the element, scroll into view, and then move the mouse cursor to the center of the element (see http://www.google.com/codesearch#2tHw6m3DZzo/trunk/javascript/atoms/dom.js). You can look at how the Windows driver's mouseMove is implemented here:
http://www.google.com/codesearch#2tHw6m3DZzo/trunk/cpp/webdriver-interactions/interactions.cpp

It turns out that hover states for Windows in Selenium 2 are just problematic right now. You can even see inside the Selenium 2 test suite that hover states are not skipped: for Windows-based systems:

http://www.google.com/codesearch#2tHw6m3DZzo/trunk/java/client/test/org/openqa/selenium/RenderedWebElementTest.java&q=2067%20package:http://selenium\.googlecode\.com

if (!supportsHover()) {       
  System.out.println("Skipping hover test: Hover is very short-lived on Windows. Issue 2067.");       
  return;
}

The full bug report is here:
http://code.google.com/p/selenium/issues/detail?id=2067

In Selenium v2.15.0, even the Internet Explorer wiki was updated to remind people that hover states (using mousemove) have issues:

http://code.google.com/p/selenium/source/diff?spec=svn14947&r=14947&format=side&path=/wiki/InternetExplorerDriver.wiki

The workaround seems to be generating your own synthetic events:

$('#myelem').trigger('mouseenter');