The JCrypTool Tests repository contains all JCrypTool test fragments and plug-ins. None of these projects is working without it's corresponding main plug-in available in the JCrypTool Core or JCrypTool Crypto repository.
Have a look at our wiki for more information, especially the Getting started as a JCrypTool Developer page. Feel free to ask any question you might have in our developers group.
JCrypTool downloads are available as weekly builds (unstable) and as release builds (stable).
General information on the CrypTool and JCrypTool projects is available in the CrypTool portal.