@Override
    public void beforeSendMessage(ClusterDistributionManager dm, DistributionMessage message) {
      if (message instanceof ParallelQueueRemovalMessage) {
        numberOfSentPQRM.addAndGet(message.getRecipients().size());
      }
    }
Put entries in region after gateway sender is stopped. Count number of PQRM messages sent.
geode-wan/src/distributedTest/java/org/apache/geode/internal/cache/wan/parallel/ParallelGatewaySenderOperationsDistributedTest.java