in src/it/scala/com/gu/kinesis/Inspectable.scala [95:101]
private def checkpointCountByShardConsumer(): MapView[ShardConsumerId, Int] = {
checkpointEventsByShardConsumer.asScala.toIndexedSeq
.filter { case (_, event) => event == CheckpointAcked }
.groupBy { case (key, _) => key }
.view
.mapValues(_.size)
}