private IncomingMessageEnvelope createIncomingMessageEnvelope(CoordinatorStreamMessage message, SystemStreamPartition ssp) {
    try {
      byte[] key = SamzaObjectMapper.getObjectMapper().writeValueAsString(message.getKeyArray()).getBytes("UTF-8");
      byte[] value = SamzaObjectMapper.getObjectMapper().writeValueAsString(message.getMessageMap()).getBytes("UTF-8");
      return new IncomingMessageEnvelope(ssp, null, key, value);
    } catch (Exception e) {
      return null;
    }
  }
Verify that if a particular key-value is written, then another, then the original again,
that the original occurs last in the set.
samza-core/src/test/java/org/apache/samza/coordinator/stream/TestCoordinatorStreamSystemConsumer.java