StepExecutionSplitter stepExecutionSplitter = mock(StepExecutionSplitter.class);
MessagingOperations operations = mock(MessagingOperations.class);
Message message = mock(Message.class);
//when
when(message.getPayload()).thenReturn(Collections.emptyList());
when(operations.receive((PollableChannel) anyObject())).thenReturn(message);
//set
messageChannelPartitionHandler.setMessagingOperations(operations);
//execute
Collection<StepExecution> executions = messageChannelPartitionHandler.handle(stepExecutionSplitter, masterStepExecution);