Fixed #10853 -- Skipped some sessions tests with dummy cache backend

from django.contrib.sessions.backends.signed_cookies import SessionStore as CookieSession

from django.contrib.sessions.models import Session

from django.contrib.sessions.middleware import SessionMiddleware

from django.core.cache import DEFAULT_CACHE_ALIAS

from django.core.exceptions import ImproperlyConfigured, SuspiciousOperation

from django.http import HttpResponse

from django.test import TestCase, RequestFactory

        self.assertTrue(self.session.modified)

    def test_save(self):

        if (hasattr(self.session, '_cache') and

                'DummyCache' in settings.CACHES[DEFAULT_CACHE_ALIAS]['BACKEND']):

            raise unittest.SkipTest("Session saving tests require a real cache backend")

        self.session.save()

        self.assertTrue(self.session.exists(self.session.session_key))

    backend = CacheDBSession

    @unittest.skipIf('DummyCache' in settings.CACHES[DEFAULT_CACHE_ALIAS]['BACKEND'],

        "Session saving tests require a real cache backend")

    def test_exists_searches_cache_first(self):

        self.session.save()

        with self.assertNumQueries(0):