in src/it/scala/com/gu/kinesis/KinesisSourceTest.scala [261:271]
private def assertRebalancingTestConditions(
receivedByConsumer1: IndexedSeq[KeyAndMessage],
receivedByConsumer2: IndexedSeq[KeyAndMessage]
): Unit = {
val receivedByConsumer1Only = receivedByConsumer1.toSet -- receivedByConsumer2.toSet
val receivedByConsumer2Only = receivedByConsumer2.toSet -- receivedByConsumer1.toSet
val receivedByBoth = receivedByConsumer1.toSet.intersect(receivedByConsumer2.toSet)
receivedByConsumer1Only should not be empty
receivedByConsumer2Only should not be empty
}