diff --git a/system_tests/test_grpc.py b/system_tests/test_grpc.py
index 4bf1c5b..365bc91 100644
--- a/system_tests/test_grpc.py
+++ b/system_tests/test_grpc.py
@@ -39,7 +39,7 @@
     list(list_topics_iter)
 
 
-def test_grpc_request_with_jwt_credentials(http_request):
+def test_grpc_request_with_jwt_credentials():
     credentials, project_id = google.auth.default()
     audience = 'https://{}/google.pubsub.v1.Publisher'.format(
         publisher_client.PublisherClient.SERVICE_ADDRESS)
@@ -49,7 +49,27 @@
 
     channel = google.auth.transport.grpc.secure_authorized_channel(
         credentials,
-        http_request,
+        None,
+        publisher_client.PublisherClient.SERVICE_ADDRESS)
+
+    # Create a pub/sub client.
+    client = publisher_client.PublisherClient(channel=channel)
+
+    # list the topics and drain the iterator to test that an authorized API
+    # call works.
+    list_topics_iter = client.list_topics(
+        project='projects/{}'.format(project_id))
+    list(list_topics_iter)
+
+
+def test_grpc_request_with_on_demand_jwt_credentials():
+    credentials, project_id = google.auth.default()
+    credentials = google.auth.jwt.OnDemandCredentials.from_signing_credentials(
+        credentials)
+
+    channel = google.auth.transport.grpc.secure_authorized_channel(
+        credentials,
+        None,
         publisher_client.PublisherClient.SERVICE_ADDRESS)
 
     # Create a pub/sub client.