private static CheckpointV1 buildCheckpointV1(SystemStreamPartition ssp, String offset) {
    return new CheckpointV1(ImmutableMap.of(ssp, offset));
  }
Create a new {@link SystemConsumer} that returns a list of messages sequentially at each subsequent poll.

@param pollOutputs a list of poll outputs to be returned at subsequent polls.
                   The i'th call to consumer.poll() will return the list at pollOutputs[i]
samza-kafka/src/test/java/org/apache/samza/checkpoint/kafka/TestKafkaCheckpointManager.java