It feels like you wish to test your client side code that calls real
server side code, isn't it ?
If you would like to test your client side code that really calls the
server side code, it will be the case if you start a GWTTestCase.
You could not have a server test with a client side test despite you
are using an MVP approach.
client side code use some GWT.create that are not understood from
javac and server side code contains code not understood by
GWTTestCase...