ATS Mimic enables developers to test their composer WITHOUT an Application Server or a Browser. Through this library, testers can mimic user interactions to applications such as clicking or typing to verify composer's (controller layer) data and logic. All they have to do is to write a regular unit test case and use Mimic's utility class to interact components on ZUL and then, run the test case.
Check out how: http://books.zkoss.org/wiki/Small_Talks/2012/April/Shining_ZATS_Mimic