Fix cname_lookup test

c.badtest.com actually has a CNAME now, and apparently we're actually
doing the look-up during tests.

Change-Id: I306b7d05740a2b8fcef2f5f432ebf5211bc723cc
(cherry picked from commit 54fc8a7dee)

test/unit/common/middleware/test_cname_lookup.py

@@ -305,7 +305,9 @@ class TestCNAMELookup(unittest.TestCase):
         resp = do_test('c.badtest.com')
         self.assertEqual(resp, bad_domain)
 
-    def test_host_is_storage_domain(self):
+    @mock.patch('dns.resolver.Resolver.query',
+                side_effect=dns.exception.DNSException)
+    def test_host_is_storage_domain(self, mock_lookup):
         conf = {'storage_domain': 'storage.example.com',
                 'lookup_depth': 2}
         app = cname_lookup.CNAMELookupMiddleware(FakeApp(), conf)
@@ -318,9 +320,12 @@ class TestCNAMELookup(unittest.TestCase):
         bad_domain = [b'CNAME lookup failed to resolve to a valid domain']
         resp = do_test('c.badtest.com')
         self.assertEqual(resp, bad_domain)
+        self.assertEqual(1, len(mock_lookup.mock_calls))
+        mock_lookup.reset_mock()
 
         resp = do_test('storage.example.com')
         self.assertEqual(resp, [b'FAKE APP'])
+        self.assertEqual(0, len(mock_lookup.mock_calls))
 
     def test_resolution_to_storage_domain_exactly(self):
         conf = {'storage_domain': 'example.com',