Test Speedup: Isolate Modulestore Signals

There are a number of Django Signals that are on the modulestore's
SignalHandler class, such as SignalHandler.course_published. These
signals can trigger very expensive processes to occur, such as course
overview or block structures generation. Most of the time, the test
author doesn't care about these side-effects.

This commit does a few things:

* Converts the signals on SignalHandler to be instances of a new
  SwitchedSignal class, that allows signal sending to be disabled.

* Creates a SignalIsolationMixin helper similar in spirit to the
  CacheIsolationMixin, and adds it to the ModuleStoreIsolationMixin
  (and thus to ModuleStoreTestCase and SharedModuleStoreTestCase).

* Converts our various tests to use this new mechanism. In some cases,
  this means adjusting query counts downwards because they no longer
  have to account for publishing listener actions.

Modulestore generated signals are now muted by default during test runs.
Calls to send() them will result in no-ops. You can choose to enable
specific signals for a given subclass of ModuleStoreTestCase or
SharedModuleStoreTestCase by specifying an ENABLED_SIGNALS class
attribute, like the following example:

    from xmodule.modulestore.tests.django_utils import ModuleStoreTestCase

    class MyPublishTestCase(ModuleStoreTestCase):
        ENABLED_SIGNALS = ['course_published', 'pre_publish']

You should take great care when disabling signals outside of a
ModuleStoreTestCase or SharedModuleStoreTestCase, since they can leak
out into other tests. Be sure to always clean up, and never disable
signals outside of testing. Because signals are essentially process
globals, it can have a lot of unpleasant side-effects if we start
mucking around with them during live requests.

Overall, this change has cut the total test execution time for
edx-platform by a bit over a third, though we still spend a lot in
pre-test setup during our test builds.

[PERF-413]

openedx/core/djangoapps/bookmarks/tests/test_api.py

@@ -43,7 +43,6 @@ class BookmarksAPITests(BookmarkApiEventTestMixin, BookmarksTestsBase):
     """
     These tests cover the parts of the API methods.
     """
-
     def setUp(self):
         super(BookmarksAPITests, self).setUp()
 
@@ -123,7 +122,7 @@ class BookmarksAPITests(BookmarkApiEventTestMixin, BookmarksTestsBase):
         """
         self.assertEqual(len(api.get_bookmarks(user=self.user, course_key=self.course.id)), 2)
 
-        with self.assertNumQueries(10):
+        with self.assertNumQueries(9):
             bookmark_data = api.create_bookmark(user=self.user, usage_key=self.vertical_2.location)
 
         self.assert_bookmark_event_emitted(
@@ -144,7 +143,7 @@ class BookmarksAPITests(BookmarkApiEventTestMixin, BookmarksTestsBase):
         """
         self.assertEqual(len(api.get_bookmarks(user=self.user, course_key=self.course.id)), 2)
 
-        with self.assertNumQueries(10):
+        with self.assertNumQueries(9):
             bookmark_data = api.create_bookmark(user=self.user, usage_key=self.vertical_2.location)
 
         self.assert_bookmark_event_emitted(

openedx/core/djangoapps/bookmarks/tests/test_models.py

@@ -253,10 +253,10 @@ class BookmarkModelTests(BookmarksTestsBase):
 
     @ddt.data(
         (ModuleStoreEnum.Type.mongo, 'course', [], 3),
-        (ModuleStoreEnum.Type.mongo, 'chapter_1', [], 4),
-        (ModuleStoreEnum.Type.mongo, 'sequential_1', ['chapter_1'], 6),
-        (ModuleStoreEnum.Type.mongo, 'vertical_1', ['chapter_1', 'sequential_1'], 8),
-        (ModuleStoreEnum.Type.mongo, 'html_1', ['chapter_1', 'sequential_2', 'vertical_2'], 10),
+        (ModuleStoreEnum.Type.mongo, 'chapter_1', [], 3),
+        (ModuleStoreEnum.Type.mongo, 'sequential_1', ['chapter_1'], 4),
+        (ModuleStoreEnum.Type.mongo, 'vertical_1', ['chapter_1', 'sequential_1'], 6),
+        (ModuleStoreEnum.Type.mongo, 'html_1', ['chapter_1', 'sequential_2', 'vertical_2'], 7),
         (ModuleStoreEnum.Type.split, 'course', [], 3),
         (ModuleStoreEnum.Type.split, 'chapter_1', [], 2),
         (ModuleStoreEnum.Type.split, 'sequential_1', ['chapter_1'], 2),

openedx/core/djangoapps/bookmarks/tests/test_services.py

@@ -68,7 +68,7 @@ class BookmarksServiceTests(BookmarksTestsBase):
                 self.bookmark_service.set_bookmarked(usage_key=UsageKey.from_string("i4x://ed/ed/ed/interactive"))
             )
 
-        with self.assertNumQueries(10):
+        with self.assertNumQueries(9):
             self.assertTrue(self.bookmark_service.set_bookmarked(usage_key=self.vertical_2.location))
 
     def test_unset_bookmarked(self):

openedx/core/djangoapps/bookmarks/tests/test_tasks.py

@@ -20,6 +20,7 @@ class XBlockCacheTaskTests(BookmarksTestsBase):
     """
     Test the XBlockCache model.
     """
+
     def setUp(self):
         super(XBlockCacheTaskTests, self).setUp()
 
@@ -157,12 +158,6 @@ class XBlockCacheTaskTests(BookmarksTestsBase):
         """
         course = getattr(self, course_attr)
 
-        if settings.ROOT_URLCONF == 'lms.urls':
-            # When the tests run under LMS, there is a certificates course_published
-            # signal handler that runs and causes the number of queries to be one more
-            # (due to the check for disabled_xblocks in django.py).
-            expected_sql_queries += 1
-
         with self.assertNumQueries(expected_sql_queries):
             _update_xblocks_cache(course.id)
 

openedx/core/djangoapps/content/block_structure/tests/test_signals.py

@@ -19,6 +19,8 @@ class CourseBlocksSignalTest(ModuleStoreTestCase):
     """
     Tests for the Course Blocks signal
     """
+    ENABLED_SIGNALS = ['course_deleted', 'course_published']
+
     def setUp(self):
         super(CourseBlocksSignalTest, self).setUp()
         self.course = CourseFactory.create()

openedx/core/djangoapps/content/course_overviews/tests.py

@@ -52,6 +52,8 @@ class CourseOverviewTestCase(ModuleStoreTestCase):
 
     COURSE_OVERVIEW_TABS = {'courseware', 'info', 'textbooks', 'discussion', 'wiki', 'progress'}
 
+    ENABLED_SIGNALS = ['course_deleted', 'course_published']
+
     def check_course_overview_against_course(self, course):
         """
         Compares a CourseOverview object against its corresponding

openedx/core/djangoapps/content/course_structures/api/v0/tests_api.py

@@ -18,6 +18,8 @@ class CourseStructureApiTests(ModuleStoreTestCase):
 
     ENABLED_CACHES = ['default', 'mongo_metadata_inheritance', 'loc_cache']
 
+    ENABLED_SIGNALS = ['course_published']
+
     def setUp(self):
         """
         Test setup

openedx/core/djangoapps/course_groups/tests/test_cohorts.py

@@ -263,8 +263,8 @@ class TestCohorts(ModuleStoreTestCase):
         )
 
     @ddt.data(
-        (True, 3),
-        (False, 7),
+        (True, 2),
+        (False, 6),
     )
     @ddt.unpack
     def test_get_cohort_sql_queries(self, use_cached, num_sql_queries):

openedx/core/djangoapps/credit/tests/test_verification_access.py

@@ -240,6 +240,8 @@ class WriteOnPublishTest(ModuleStoreTestCase):
     """
     MODULESTORE = TEST_DATA_SPLIT_MODULESTORE
 
+    ENABLED_SIGNALS = ['course_published', 'pre_publish']
+
     @patch.dict(settings.FEATURES, {"ENABLE_COURSEWARE_INDEX": False})
     def setUp(self):
         super(WriteOnPublishTest, self).setUp()