Fix check_sa_exists not checking all service accounts in python libra…

…ry (kubeflow#718)

* Fix check_sa_exists not checking all service accounts

* Fixed lint errors

python/kfserving/kfserving/api/creds_utils.py

@@ -179,9 +179,7 @@ def check_sa_exists(namespace, service_account):
     '''Check if the specified service account existing.'''
     sa_list = client.CoreV1Api().list_namespaced_service_account(namespace=namespace)
 
-    sa_name_list = []
-    for item in range(0, len(sa_list.items)-1):
-        sa_name_list.append(sa_list.items[item].metadata.name)
+    sa_name_list = [sa.metadata.name for sa in sa_list.items]
 
     if service_account in sa_name_list:
         return True

python/kfserving/test/test_creds_utils.py

@@ -0,0 +1,19 @@
+from unittest import mock
+
+from kubernetes.client import V1ServiceAccountList, V1ServiceAccount, V1ObjectMeta
+
+from kfserving.api.creds_utils import check_sa_exists
+
+
+@mock.patch('kubernetes.client.CoreV1Api.list_namespaced_service_account')
+def test_check_sa_exists(mock_client):
+    # Mock kubernetes client to return 2 accounts
+    accounts = V1ServiceAccountList(
+        items=[V1ServiceAccount(metadata=V1ObjectMeta(name=n)) for n in ['a', 'b']]
+    )
+    mock_client.return_value = accounts
+
+    # then a, b should exist, c should not
+    assert check_sa_exists('kubeflow', 'a') is True
+    assert check_sa_exists('kubeflow', 'b') is True
+    assert check_sa_exists('kubeflow', 'c') is False