Add google.oauth2.credentials.Credentials.from_authorized_user_file (#226)

diff --git a/tests/test__cloud_sdk.py b/tests/test__cloud_sdk.py
index c14fc20..58c7270 100644
--- a/tests/test__cloud_sdk.py
+++ b/tests/test__cloud_sdk.py
@@ -145,7 +145,8 @@
     assert credentials._client_id == AUTHORIZED_USER_FILE_DATA['client_id']
     assert (credentials._client_secret ==
             AUTHORIZED_USER_FILE_DATA['client_secret'])
-    assert credentials._token_uri == _cloud_sdk._GOOGLE_OAUTH2_TOKEN_ENDPOINT
+    assert (credentials._token_uri ==
+            google.oauth2.credentials._GOOGLE_OAUTH2_TOKEN_ENDPOINT)
 
 
 def test_load_authorized_user_credentials_bad_format():