Add a TestCase mixin for enabling caches in tests

By default, disable all caching in tests, to preserve test independence.
In order to enable caching, inherit from CacheSetupMixin, and specify
which cache configuration is needed.

[EV-32]

lms/djangoapps/django_comment_client/base/tests.py

@@ -10,7 +10,6 @@ from django.test.client import RequestFactory
 from django.contrib.auth.models import User
 from django.core.management import call_command
 from django.core.urlresolvers import reverse
-from request_cache.middleware import RequestCache
 from mock import patch, ANY, Mock
 from nose.tools import assert_true, assert_equal
 from nose.plugins.attrib import attr
@@ -24,8 +23,9 @@ from django_comment_client.tests.utils import CohortedTestCase
 from django_comment_client.tests.unicode import UnicodeTestMixin
 from django_comment_common.models import Role
 from django_comment_common.utils import seed_permissions_roles, ThreadContext
-from student.tests.factories import CourseEnrollmentFactory, UserFactory, CourseAccessRoleFactory
+
 from lms.djangoapps.teams.tests.factories import CourseTeamFactory, CourseTeamMembershipFactory
+from student.tests.factories import CourseEnrollmentFactory, UserFactory, CourseAccessRoleFactory
 from util.testing import UrlResetMixin
 from xmodule.modulestore.tests.factories import CourseFactory, ItemFactory
 from xmodule.modulestore.tests.django_utils import ModuleStoreTestCase, SharedModuleStoreTestCase
@@ -351,17 +351,12 @@ class ViewsTestCaseMixin(object):
 class ViewsQueryCountTestCase(UrlResetMixin, ModuleStoreTestCase, MockRequestSetupMixin, ViewsTestCaseMixin):
 
     CREATE_USER = False
+    ENABLED_CACHES = ['default', 'mongo_metadata_inheritance', 'loc_cache']
 
     @patch.dict("django.conf.settings.FEATURES", {"ENABLE_DISCUSSION_SERVICE": True})
     def setUp(self):
         super(ViewsQueryCountTestCase, self).setUp()
 
-    def clear_caches(self):
-        """Clears caches so that query count numbers are accurate."""
-        for cache in settings.CACHES:
-            caches[cache].clear()
-        RequestCache.clear_request_cache()
-
     def count_queries(func):  # pylint: disable=no-self-argument
         """
         Decorates test methods to count mongo and SQL calls for a