@SuppressWarnings("unchecked")
        @Override
        public Response process(Request request, Execution execution) {
            Response response = execution.process(request);
            int dataCount = countData(response.data());
            response.data().add(new StringData(request, prefix + "Data count: " + dataCount));
            return response;
        }
The prefix "[name] " is prepended to the string data
container-core/src/test/java/com/yahoo/processing/test/ProcessorLibrary.java