Delays or enforcing an execution order doesn't help. I think the problem is
"[WARN] 404 - POST /dp.verp.planer.Planer.JUnit/gwtRequest (192.168.1.51) 1424 bytes"
If I'd get this message in DevMode I'd fix web.xml's servlet-mapping but what's the equivalent of the servlet-mapping when using GWTTestCase? The WARN message occurs exactly when calling fire(). When calling fire() always
@Override
public void onFailure(ServerFailure error) {
}
is entered, instead of
@Override
public void onSuccess(MyType response) {