private byte[] serialize(Object obj) {
      try {
        return SamzaObjectMapper.getObjectMapper().writeValueAsString(obj).getBytes("UTF-8");
      } catch (Exception e) {
        throw new SamzaException(e);
      }
    }
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