I'm trying to figure out how to add entities and  spawn them with using a mod item.  Nothing happens though manual testing when I use the item on a block, nor can I spawn it directly with the summon command since its as though the entity was never actually registered. I have confirmed that  its executing  the required registration commands for both client and server.

See mod project for details: https://github.com/jshultz/WagonsMod

The best way to debug things like this is to either trace them in debug mode in Eclipse or put a bunch of System.out.println() statements throughout your code and watch the console output to understand how your code is executing.

 

For example, to know that the EntityHorseCart is actually being created you can put a System.out.println("Constructing") statement in the constructor. You should do a similar thing in your render class, maybe putting statements in your doRender() method.

 

When an entity doesn't seem to spawn, it often is spawning but just invisible or sometimes it is in a location like 0, 0, 0 that cannot be seen.

 

But anyway, use print statements in order to figure out which parts of your code are actually running.