diff --git a/django/db/utils.py b/django/db/utils.py
index 01b46a1af00..4fb75e31503 100644
--- a/django/db/utils.py
+++ b/django/db/utils.py
@@ -210,7 +210,7 @@ class ConnectionHandler(object):
                         "Connection '%s' has mismatched TEST and TEST_* "
                         "database settings." % alias)
             else:
-                test_settings = old_test_settings
+                test_settings.update(old_test_settings)
                 for key, _ in six.iteritems(old_test_settings):
                     warnings.warn("In Django 1.9 the %s connection setting will be moved "
                                   "to a %s entry in the TEST setting" %
diff --git a/tests/backends/tests.py b/tests/backends/tests.py
index 83ed099a9bf..9742358a59f 100644
--- a/tests/backends/tests.py
+++ b/tests/backends/tests.py
@@ -26,7 +26,7 @@ from django.db.models.sql.constants import CURSOR
 from django.db.utils import ConnectionHandler
 from django.test import (TestCase, TransactionTestCase, override_settings,
     skipUnlessDBFeature, skipIfDBFeature)
-from django.test.utils import str_prefix
+from django.test.utils import str_prefix, IgnoreAllDeprecationWarningsMixin
 from django.utils import six
 from django.utils.six.moves import xrange
 
@@ -1080,12 +1080,19 @@ class BackendUtilTests(TestCase):
               '0')
 
 
-class DBTestSettingsRenamedTests(TestCase):
+class DBTestSettingsRenamedTests(IgnoreAllDeprecationWarningsMixin, TestCase):
 
     mismatch_msg = ("Connection 'test-deprecation' has mismatched TEST "
                     "and TEST_* database settings.")
 
+    @classmethod
+    def setUpClass(cls):
+        # Silence "UserWarning: Overriding setting DATABASES can lead to
+        # unexpected behavior."
+        cls.warning_classes.append(UserWarning)
+
     def setUp(self):
+        super(DBTestSettingsRenamedTests, self).setUp()
         self.handler = ConnectionHandler()
         self.db_settings = {'default': {}}