fix: convert exam update into a lambda on commit

Current behavior for both old and new exams paths on exam creation is
that the signal fires, the update code kicks off a celery task which
looks for a new exam, and that exam is not found so no actual update
is done. Or the old version is visible but the updated version is not.

By waiting until the change is actually committed, we should find the
new exam when we search for it.

This is currently an invisible bug just because of the large numbers
of updates that working on a course provides, the exam will be correct
unless it was the absolute last thing that was touched, in which case
it will be out of date.

cms/djangoapps/contentstore/signals/handlers.py

@@ -125,9 +125,9 @@ def listen_for_course_publish(sender, course_key, **kwargs):  # pylint: disable=
         dump_course_to_neo4j
     )
 
-    # register special exams asynchronously
+    # register special exams asynchronously after the data is ready
     course_key_str = str(course_key)
-    update_special_exams_and_publish.delay(course_key_str)
+    transaction.on_commit(lambda: update_special_exams_and_publish.delay(course_key_str))
 
     if key_supports_outlines(course_key):
         # Push the course outline to learning_sequences asynchronously.

cms/djangoapps/contentstore/tests/test_exams.py

@@ -2,7 +2,7 @@
 Test the exams service integration into Studio
 """
 from datetime import datetime, timedelta
-from unittest.mock import patch
+from unittest.mock import patch, Mock
 
 import ddt
 from django.conf import settings
@@ -19,6 +19,8 @@ from xmodule.modulestore.tests.factories import CourseFactory, ItemFactory
 @override_waffle_flag(EXAMS_IDA, active=True)
 @patch.dict('django.conf.settings.FEATURES', {'ENABLE_SPECIAL_EXAMS': True})
 @patch('cms.djangoapps.contentstore.exams._patch_course_exams')
+@patch('cms.djangoapps.contentstore.signals.handlers.transaction.on_commit',
+       new=Mock(side_effect=lambda func: func()),)  # run right away
 class TestExamService(ModuleStoreTestCase):
     """
     Test for syncing exams to the exam service

cms/djangoapps/contentstore/tests/test_proctoring.py

@@ -4,7 +4,7 @@ Tests for the edx_proctoring integration into Studio
 
 
 from datetime import datetime, timedelta
-from unittest.mock import patch
+from unittest.mock import patch, Mock
 
 import ddt
 from django.conf import settings
@@ -20,6 +20,8 @@ from common.djangoapps.student.tests.factories import UserFactory
 
 @ddt.ddt
 @patch.dict('django.conf.settings.FEATURES', {'ENABLE_SPECIAL_EXAMS': True})
+@patch('cms.djangoapps.contentstore.signals.handlers.transaction.on_commit',
+       new=Mock(side_effect=lambda func: func()),)  # run right away
 class TestProctoredExams(ModuleStoreTestCase):
     """
     Tests for the publishing of proctored exams