Extract new list position validation to a method

app/services/boards/lists/move_service.rb

@@ -8,10 +8,7 @@ module Boards
 
       def execute
         return false unless list.label?
-        return false if new_position.blank?
-        return false if new_position == old_position
-        return false if new_position == first_position
-        return false if new_position == last_position
+        return false if invalid_position?
 
         list.with_lock do
           reorder_intermediate_lists
@@ -27,6 +24,12 @@ module Boards
         @list ||= board.lists.find(params[:list_id])
       end
 
+      def invalid_position?
+        return true if new_position.blank?
+
+        [old_position, first_position, last_position].include?(new_position)
+      end
+
       def first_position
         board.lists.first.try(:position)
       end