Ok, I found the solution after fiddling around some more. Apparently, since there is no EAR in the test project, there is no
application.xmlas well to instruct the container to parse the the prj-entities class folder for peristence units.
The solution is to have a persistence.xml file in the prj-test/META-INF folder and declare the presistence unit there. In this case you must also list all entities using <class> tags inside that persistence.xml. This way, the embedded JBoss will pick it up and integration tests will work.