@Override
        public void onVisitorError(String message) {
            super.onVisitorError(message);
            builder.append("onVisitorError : ").append(message).append("\n");
        }
Test that using an id.user=foo selection only tries to visit a single
superbucket for that user.
documentapi/src/test/java/com/yahoo/documentapi/messagebus/MessageBusVisitorSessionTestCase.java