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/certificates/tests/test_views.py

@@ -12,6 +12,7 @@ from django.test.client import Client
 from django.test.utils import override_settings
 from nose.plugins.attrib import attr
 from opaque_keys.edx.locator import CourseLocator
+from openedx.core.djangolib.testing.utils import CacheIsolationTestCase
 
 from certificates.api import get_certificate_url
 from certificates.models import (
@@ -38,7 +39,7 @@ FEATURES_WITH_CUSTOM_CERTS_ENABLED.update(FEATURES_WITH_CERTS_ENABLED)
 
 @attr('shard_1')
 @ddt.ddt
-class UpdateExampleCertificateViewTest(TestCase):
+class UpdateExampleCertificateViewTest(CacheIsolationTestCase):
     """Tests for the XQueue callback that updates example certificates. """
 
     COURSE_KEY = CourseLocator(org='test', course='test', run='test')
@@ -48,6 +49,8 @@ class UpdateExampleCertificateViewTest(TestCase):
     DOWNLOAD_URL = 'http://www.example.com'
     ERROR_REASON = 'Kaboom!'
 
+    ENABLED_CACHES = ['default']
+
     def setUp(self):
         super(UpdateExampleCertificateViewTest, self).setUp()
         self.cert_set = ExampleCertificateSet.objects.create(course_key=self.COURSE_KEY)