I cleared the bug that was happening during the dispatch from the endpoint to the service : it was due to a bad packaging of the service.
Indeed the wsrp lib was both in the sar file and in the war/WEB-INF/lib and classes from the endpoint were just different from those of the service. The dynamic invocation was not happening because of that.
I removed the extension from WSRPInvocation from the ServerInvocation, etc...
Also I removed the ServiceDescriptionEndpoint JMXization because it is simply not an MBean service (and thus does not need to extends AbstractJBossService and is not declared in jboss-service.xml) because it is a POJO created by the WS layer.
Now when the test is invoked it produces another exception due to a class cast exception but this is a business error of the current wsrp operation execution.