diff --git a/tests/rest/client/v1/test_rooms.py b/tests/rest/client/v1/test_rooms.py
index de376fb51..9f3725538 100644
--- a/tests/rest/client/v1/test_rooms.py
+++ b/tests/rest/client/v1/test_rooms.py
@@ -515,9 +515,6 @@ class RoomsCreateTestCase(RestTestCase):
 
         synapse.rest.client.v1.room.register_servlets(hs, self.mock_resource)
 
-    def tearDown(self):
-        pass
-
     @defer.inlineCallbacks
     def test_post_room_no_keys(self):
         # POST with no config keys, expect new room id
diff --git a/tests/unittest.py b/tests/unittest.py
index 38715972d..7b478c429 100644
--- a/tests/unittest.py
+++ b/tests/unittest.py
@@ -12,7 +12,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
+import twisted
 from twisted.trial import unittest
 
 import logging
@@ -65,6 +65,10 @@ class TestCase(unittest.TestCase):
 
         @around(self)
         def setUp(orig):
+            # enable debugging of delayed calls - this means that we get a
+            # traceback when a unit test exits leaving things on the reactor.
+            twisted.internet.base.DelayedCall.debug = True
+
             old_level = logging.getLogger().level
 
             if old_level != level:
diff --git a/tests/utils.py b/tests/utils.py
index ed8a7360f..44e5f7509 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -58,6 +58,10 @@ def setup_test_homeserver(name="test", datastore=None, config=None, **kargs):
         config.email_enable_notifs = False
         config.block_non_admin_invites = False
 
+        # disable user directory updates, because they get done in the
+        # background, which upsets the test runner.
+        config.update_user_directory = False
+
     config.use_frozen_dicts = True
     config.database_config = {"name": "sqlite3"}
     config.ldap_enabled = False