Only delete latest grade override if it came from proctoring

... on proctored exam attempt deletion

JIRA:EDUCATOR-4642

lms/djangoapps/grades/api.py

@@ -65,6 +65,7 @@ def override_subsection_grade(
         requesting_user=overrider,
         subsection_grade_model=grade,
         feature=feature,
+        system=feature,
         earned_all_override=earned_all,
         earned_graded_override=earned_graded,
     )
@@ -93,6 +94,10 @@ def undo_override_subsection_grade(user_id, course_key_or_id, usage_key_or_id, f
 
     Fires off a recalculate_subsection_grade async task to update the PersistentSubsectionGrade table. If the
     override does not exist, no error is raised, it just triggers the recalculation.
+
+    feature: if specified, the deletion will only occur if the
+             override to be deleted was created by the corresponding
+             subsystem
     """
     course_key = _get_key(course_key_or_id, CourseKey)
     usage_key = _get_key(usage_key_or_id, UsageKey)
@@ -102,8 +107,8 @@ def undo_override_subsection_grade(user_id, course_key_or_id, usage_key_or_id, f
     except ObjectDoesNotExist:
         return
 
-    # Older rejected exam attempts that transition to verified might not have an override created
-    if override is not None:
+    if override is not None and (
+            not feature or feature == override.system):
         override.delete(feature=feature)
 
     # Cache a new event id and event type which the signal handler will use to emit a tracking log event.

lms/djangoapps/grades/constants.py

@@ -15,3 +15,4 @@ class ScoreDatabaseTableEnum(object):
 class GradeOverrideFeatureEnum(object):
     proctoring = 'PROCTORING'
     gradebook = 'GRADEBOOK'
+    grade_import = 'grade-import'

lms/djangoapps/grades/tests/test_services.py

@@ -259,7 +259,10 @@ class GradesServiceTests(ModuleStoreTestCase):
 
     @freeze_time('2017-01-01')
     def test_undo_override_subsection_grade(self):
-        override, _ = PersistentSubsectionGradeOverride.objects.update_or_create(grade=self.grade)
+        override, _ = PersistentSubsectionGradeOverride.objects.update_or_create(
+            grade=self.grade,
+            system=GradeOverrideFeatureEnum.proctoring
+        )
         override_id = override.id
         self.service.undo_override_subsection_grade(
             user_id=self.user.id,
@@ -286,6 +289,26 @@ class GradesServiceTests(ModuleStoreTestCase):
         override_history = PersistentSubsectionGradeOverrideHistory.objects.filter(override_id=override_id).first()
         self._verify_override_history(override_history, PersistentSubsectionGradeOverrideHistory.DELETE)
 
+    def test_undo_override_subsection_grade_across_features(self):
+        """
+        Test that deletion of subsection grade overrides requested by
+        one feature doesn't delete overrides created by another
+        feature.
+        """
+        override, _ = PersistentSubsectionGradeOverride.objects.update_or_create(
+            grade=self.grade,
+            system=GradeOverrideFeatureEnum.gradebook
+        )
+        self.service.undo_override_subsection_grade(
+            user_id=self.user.id,
+            course_key_or_id=self.course.id,
+            usage_key_or_id=self.subsection.location,
+            feature=GradeOverrideFeatureEnum.proctoring,
+        )
+
+        override = self.service.get_subsection_grade_override(self.user.id, self.course.id, self.subsection.location)
+        self.assertIsNotNone(override)
+
     @freeze_time('2018-01-01')
     def test_undo_override_subsection_grade_without_grade(self):
         """