diff --git a/nova/tests/unit/test_exception.py b/nova/tests/unit/test_exception.py
index 6b1617047c..3b54f485d9 100644
--- a/nova/tests/unit/test_exception.py
+++ b/nova/tests/unit/test_exception.py
@@ -123,8 +123,12 @@ class NovaExceptionTestCase(test.NoDBTestCase):
         class FakeNovaException_Remote(exception.NovaException):
             msg_fmt = "some message"
 
-            def __unicode__(self):
-                return u"print the whole trace"
+            if six.PY3:
+                def __str__(self):
+                    return "print the whole trace"
+            else:
+                def __unicode__(self):
+                    return u"print the whole trace"
 
         exc = FakeNovaException_Remote()
         self.assertEqual(six.text_type(exc), u"print the whole trace")
diff --git a/tox.ini b/tox.ini
index feb52884b1..4b0ca84605 100644
--- a/tox.ini
+++ b/tox.ini
@@ -36,6 +36,7 @@ deps = -r{toxinidir}/requirements.txt
 commands =
   find . -type f -name "*.pyc" -delete
   python -m testtools.run \
+    nova.tests.unit.test_exception \
     nova.tests.unit.db.test_db_api \
     nova.tests.unit.test_versions \
     nova.tests.unit.objects.test_agent \