GWTTest java.lang.NullPointerException cannot invoke because "this.service" is null

Question

I've a problem with GWT unit test, this is the code

    StudenteServiceAsync service;

    public void gwtSetUp(){
        // Create the service that we will test.
        service = GWT.create(StudenteService.class);
        ServiceDefTarget target = (ServiceDefTarget) service;
        target.setServiceEntryPoint(GWT.getModuleBaseURL() + "progettosweng/studenti");
    }

    @Override
    public String getModuleName() {
        return "com.university";
    }

    @Test
    public synchronized void getNumeroStudenti() throws Exception {
        delayTestFinish(10000);
        service.getNumeroStudenti(new AsyncCallback<Integer>() {
            @Override
            public void onFailure(Throwable caught) {
                fail("FAIL: getNumeroStudenti");
            }

            @Override
            public void onSuccess(Integer result) {
                assertTrue(true);
            }
        });
    }
} 

when start test, it gives me an error:

java.lang.NullPointerException: Cannot invoke "com.university.client.services.StudenteServiceAsync.getNumeroStudenti(com.google.gwt.user.client.rpc.AsyncCallback)" because "this.service" is null

For me the error is never go in gwtSetUp() and the service is ever null. what should I do? thanks