refactor test case: test_robot_could_not_pick_bag_when_ticket_is_invalid
create test case: test_robot_could_not_pick_bag_when_ticket_is_already_used
create test case: test_robot_could_not_pick_bag_when_ticket_has_be_returned_by_cabinet
create test case: test_cabinet_could_not_pick_bag_when_ticket_has_been_returned_by_robot
refactor step 1
refactor step2
refactor 3