Update test_discovery.py

tests/test_discovery.py

diff --git a/tests/test_discovery.py b/tests/test_discovery.py
index f5da46b..217f69d 100644
--- a/tests/test_discovery.py
+++ b/tests/test_discovery.py
@@ -535,7 +535,7 @@
         plus = build_from_document(
             discovery, 
             client_options={"api_endpoint": api_endpoint},
-            credentials=self.MOCK_CREDENTIAL
+            credentials=self.MOCK_CREDENTIALS
         )
 
         self.assertEqual(plus._baseUrl, api_endpoint)