Add test for Failure to select a valid command

src/test/java/com/onarandombox/MultiverseCore/test/TestWorldStuff.java

@@ -204,6 +204,9 @@ public class TestWorldStuff {
             fail("Mode property did not exist.");
         }
 
+        plugin.onCommand(mockCommandSender, mockCommand, "", new String[]{ "modify", "set", "blah", "fish", "world" });
+        verify(mockCommandSender).sendMessage(ChatColor.RED + "Sorry, You can't set: '"+ChatColor.GRAY+ "blah" + ChatColor.RED + "'");
+
     }
 
     private void createInitialWorlds(Plugin plugin, Command command) {