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/verify_student/tests/test_fake_software_secure.py

@@ -14,7 +14,7 @@ class SoftwareSecureFakeViewTest(UrlResetMixin, TestCase):
     """
     Base class to test the fake software secure view.
     """
-    
+
     URLCONF_MODULES = ['verify_student.urls']
 
     def setUp(self, **kwargs):

lms/djangoapps/verify_student/tests/test_models.py

@@ -18,6 +18,7 @@ from xmodule.modulestore.tests.django_utils import ModuleStoreTestCase
 from xmodule.modulestore.tests.factories import CourseFactory
 
 from opaque_keys.edx.keys import CourseKey
+from openedx.core.djangolib.testing.utils import CacheIsolationTestCase
 
 from lms.djangoapps.verify_student.models import (
     SoftwareSecurePhotoVerification,
@@ -844,11 +845,13 @@ class SkippedReverificationTest(ModuleStoreTestCase):
         )
 
 
-class VerificationDeadlineTest(TestCase):
+class VerificationDeadlineTest(CacheIsolationTestCase):
     """
     Tests for the VerificationDeadline model.
     """
 
+    ENABLED_CACHES = ['default']
+
     def test_caching(self):
         deadlines = {
             CourseKey.from_string("edX/DemoX/Fall"): datetime.now(pytz.UTC),