.withoutCallback should always be stubbed in testing

[Pacane]

Should change DelegateMocking to this:

    public DelegateMocking<R> useResource(R resource) {
        assert this.resource == null
                : "useResource(R) called more than once. Did you forget to call DelegateTestUtils.init()?";

        this.resource = resource;
        callbackCaptor = ArgumentCaptor.forClass(AsyncCallback.class);
        delegatingDispatchRequestCaptor = ArgumentCaptor.forClass(DelegatingDispatchRequest.class);

        when(delegate.withCallback(callbackCaptor.capture())).thenReturn(resource);
        when(delegate.withoutCallback(callbackCaptor.capture())).thenReturn(resource);
        when(delegate.withDelegatingDispatchRequest(delegatingDispatchRequestCaptor.capture())).thenReturn(delegate);

        return this;
    }

[olafleur]

@Pacane do you want to implement that?