MapStore tests, and test / fix for 2898-issue  

Are we thrown an exception ?
will an item be put into a map In the event of the backing MapStore encountering an overflow in its operation queue.
yes exception thrown at map.destroy();

java.lang.UnsupportedOperationException
	at com.hazelcast.spi.impl.ExecutionServiceImpl$ScheduledExecutorServiceDelegate.shutdown(ExecutionServiceImpl.java:427)
	at com.hazelcast.map.mapstore.writebehind.WriteBehindManager.stop(WriteBehindManager.java:49)