@Override
        public KeyValue<K, V> next() {
            final Map.Entry<K, V> entry = iter.next();
            return new KeyValue<>(entry.getKey(), entry.getValue());
        }
This class is a generic version of the in-memory key-value store that is useful for testing when you
 need a basic KeyValueStore for arbitrary types and don't have/want to write a serde
streams/src/test/java/org/apache/kafka/test/GenericInMemoryKeyValueStore.java