Fix: Display error when attempting to reset nonexistent due date extension

lms/djangoapps/instructor/tests/test_api.py

@@ -47,7 +47,8 @@ from opaque_keys.edx.locations import SlashSeparatedCourseKey
 from shoppingcart.models import CourseRegistrationCode, RegistrationCodeRedemption, Order, PaidCourseRegistration, Coupon
 from course_modes.models import CourseMode
 
-from .test_tools import msk_from_problem_urlname, get_extended_due
+from .test_tools import msk_from_problem_urlname
+from ..views.tools import get_extended_due
 
 
 @common_exceptions_400

lms/djangoapps/instructor/tests/test_tools.py

@@ -197,7 +197,7 @@ class TestSetDueDateExtension(ModuleStoreTestCase):
         self.user = user
 
         self.extended_due = functools.partial(
-            get_extended_due, course, student=user)
+            tools.get_extended_due, course, student=user)
 
     def test_set_due_date_extension(self):
         extended = datetime.datetime(2013, 12, 25, 0, 0, tzinfo=utc)
@@ -209,7 +209,7 @@ class TestSetDueDateExtension(ModuleStoreTestCase):
         extended = datetime.datetime(2013, 12, 25, 0, 0, tzinfo=utc)
         user = UserFactory.create()  # No student modules for this user
         tools.set_due_date_extension(self.course, self.week1, user, extended)
-        extended_due = functools.partial(get_extended_due, self.course, student=user)
+        extended_due = functools.partial(tools.get_extended_due, self.course, student=user)
         self.assertEqual(extended_due(self.week1), extended)
         self.assertEqual(extended_due(self.homework), extended)
 
@@ -224,8 +224,11 @@ class TestSetDueDateExtension(ModuleStoreTestCase):
             tools.set_due_date_extension(self.course, self.week3, self.user, extended)
 
     def test_reset_due_date_extension(self):
+        extended = datetime.datetime(2013, 12, 25, 0, 0, tzinfo=utc)
+        tools.set_due_date_extension(self.course, self.week1, self.user, extended)
         tools.set_due_date_extension(self.course, self.week1, self.user, None)
         self.assertEqual(self.extended_due(self.week1), None)
+        self.assertEqual(self.extended_due(self.homework), None)
 
 
 @override_settings(MODULESTORE=TEST_DATA_MIXED_MODULESTORE)
@@ -341,22 +344,6 @@ class TestDataDumps(ModuleStoreTestCase):
              "Extended Due Date": "2013-12-25 00:00"}])
 
 
-def get_extended_due(course, unit, student):
-    """
-    Get the extended due date out of a student's state for a particular unit.
-    """
-    student_module = StudentModule.objects.get(
-        student_id=student.id,
-        course_id=course.id,
-        module_state_key=unit.location
-    )
-
-    state = json.loads(student_module.state)
-    extended = state.get('extended_due', None)
-    if extended:
-        return DATE_FIELD.from_json(extended)
-
-
 def msk_from_problem_urlname(course_id, urlname, block_type='problem'):
     """
     Convert a 'problem urlname' to a module state key (db field)

lms/djangoapps/instructor/views/tools.py

@@ -159,6 +159,22 @@ def title_or_url(node):
     return title
 
 
+def get_extended_due(course, unit, student):
+    """
+    Get the extended due date out of a student's state for a particular unit.
+    """
+    student_module = StudentModule.objects.get(
+        student_id=student.id,
+        course_id=course.id,
+        module_state_key=unit.location
+    )
+
+    state = json.loads(student_module.state)
+    extended = state.get('extended_due', None)
+    if extended:
+        return DATE_FIELD.from_json(extended)
+
+
 def set_due_date_extension(course, unit, student, due_date):
     """
     Sets a due date extension. Raises DashboardError if the unit or extended
@@ -172,6 +188,10 @@ def set_due_date_extension(course, unit, student, due_date):
             raise DashboardError(_("Unit {0} has no due date to extend.").format(unit.location))
         if due_date < original_due_date:
             raise DashboardError(_("An extended due date must be later than the original due date."))
+    else:
+        # We are deleting a due date extension. Check that it exists:
+        if not get_extended_due(course, unit, student):
+            raise DashboardError(_("No due date extension is set for that student and unit."))
 
     def set_due_date(node):
         """