Don't delete misplaced items on final attempt

In assessment mode, don't delete misplaced items from the user's state
when handling the final attempt.

This is a server-side change to match what Javascript already does: upon
submitting the final attempt, misplaced items are left on the board.
However, since the corresponding state was deleted server-side, upon
refreshing the page items were returned to the bank.

drag_and_drop_v2/drag_and_drop_v2.py

@@ -403,7 +403,9 @@ class DragAndDropBlock(XBlock, XBlockWithSettingsMixin, ThemableXBlockMixin):
 
         misplaced_items = []
         for item_id in misplaced_ids:
-            del self.item_state[item_id]
+            # Don't delete misplaced item states on the final attempt.
+            if self.attempts_remain:
+                del self.item_state[item_id]
             misplaced_items.append(self._get_item_definition(int(item_id)))
 
         feedback_msgs = [FeedbackMessage(item['feedback']['incorrect'], None) for item in misplaced_items]

tests/integration/test_interaction_assessment.py

@@ -139,6 +139,36 @@ class AssessmentInteractionTest(
         for item_id in misplaced_items:
             self.assert_reverted_item(item_id)
 
+    def test_misplaced_items_not_returned_to_bank_on_final_attempt(self):
+        """
+        Test items placed on incorrect zones are not returned to item bank
+        after submitting solution on the final attempt, and remain placed after
+        subsequently refreshing the page.
+        """
+        self.place_item(0, TOP_ZONE_ID, action_key=Keys.RETURN)
+
+        # Reach final attempt
+        for _ in xrange(self.MAX_ATTEMPTS-1):
+            self.click_submit()
+
+        # Place incorrect item on final attempt
+        self.place_item(1, TOP_ZONE_ID, action_key=Keys.RETURN)
+        self.click_submit()
+
+        # Incorrect item remains placed
+        def _assert_placed(item_id, zone_title):
+            item = self._get_placed_item_by_value(item_id)
+            item_description = item.find_element_by_css_selector('.sr')
+            self.assertEqual(item_description.text, 'Placed in: {}'.format(zone_title))
+
+        _assert_placed(1, TOP_ZONE_TITLE)
+
+        # Refresh the page
+        self._page = self.go_to_page(self.PAGE_TITLE)
+
+        # Incorrect item remains placed after refresh
+        _assert_placed(1, TOP_ZONE_TITLE)
+
     def test_max_attempts_reached_submit_and_reset_disabled(self):
         """
         Test "Submit" and "Reset" buttons are disabled when no more attempts remaining

tests/unit/test_advanced.py

@@ -404,6 +404,21 @@ class AssessmentModeFixture(BaseDragAndDropAjaxFixture):
         expected_message = self._make_feedback_message(self.FINAL_FEEDBACK)
         self.assertIn(expected_message, res[self.OVERALL_FEEDBACK_KEY])
 
+    def test_do_attempt_does_not_delete_misplaced_items_at_last_attempt(self):
+        """
+        Upon submitting the final attempt, test that misplaced items are not
+        deleted from the item state.
+        """
+        self._set_final_attempt()
+        misplaced_ids = self._submit_incorrect_solution()
+
+        self.call_handler(self.DO_ATTEMPT_HANDLER, data={})
+
+        self.assertFalse(self.block.attempts_remain)  # precondition check
+
+        for i in misplaced_ids:
+            self.assertIn(str(i), self.block.item_state.keys())
+
     def test_get_user_state_does_not_include_correctness(self):
         self._submit_complete_solution()
         original_item_state = self.block.item_state