private void setShutdown(TaskCoordinator coordinator) {
      this.stopProcessing = true;
      coordinator.shutdown(TaskCoordinator.RequestScope.CURRENT_TASK);
    }
When requesting shutdown, there is no guarantee of an immediate shutdown, since there are multiple tasks in the
container. Use this flag to make sure we don't process more messages past the shutdown request in order to have
deterministic counting of the messages for the test.
samza-test/src/test/java/org/apache/samza/test/kafka/KafkaCheckpointManagerIntegrationTest.java