//execute with no default set
messageChannelPartitionHandler = new MessageChannelPartitionHandler();
//mock
StepExecution masterStepExecution = mock(StepExecution.class);
StepExecutionSplitter stepExecutionSplitter = mock(StepExecutionSplitter.class);
MessagingOperations operations = mock(MessagingOperations.class);
Message message = mock(Message.class);
PollableChannel replyChannel = mock(PollableChannel.class);
//when
when(message.getPayload()).thenReturn(Collections.emptyList());
when(operations.receive(replyChannel)).thenReturn(message);
//set
messageChannelPartitionHandler.setMessagingOperations(operations);
messageChannelPartitionHandler.setReplyChannel(replyChannel);
//execute