diff --git a/tests/testutils.py b/tests/testutils.py
index 7546595a..0827f698 100644
--- a/tests/testutils.py
+++ b/tests/testutils.py
@@ -159,6 +159,10 @@ def __init__(self):
         self._service_account_email = None
         self._token_state = credentials.TokenState.INVALID
 
+    @property
+    def universe_domain(self):
+        return 'googleapis.com'
+
     def refresh(self, request):
         self.token = 'mock-compute-engine-token'
         self._service_account_email = 'mock-gce-email'