@Override
        public void process(final Record<String, Long> record) {
            final Long oldValue = store.get(record.key());
            if (oldValue == null || record.value() > oldValue) {
                store.put(record.key(), record.value());
            }
        }
This is code sample in docs/streams/developer-guide/testing.html
streams/examples/src/test/java/org/apache/kafka/streams/examples/docs/DeveloperGuideTesting.java