Adding back "wrapped" exceptions in Refresh/Transport errors.
diff --git a/tests/test__default.py b/tests/test__default.py
index 090cea6..2df8a44 100644
--- a/tests/test__default.py
+++ b/tests/test__default.py
@@ -85,6 +85,7 @@
         _default._load_credentials_from_file(str(filename))
 
     assert excinfo.match(r'Failed to load authorized user')
+    assert excinfo.match(r'missing fields')
 
 
 def test__load_credentials_from_file_service_account():
@@ -102,6 +103,7 @@
         _default._load_credentials_from_file(str(filename))
 
     assert excinfo.match(r'Failed to load service account')
+    assert excinfo.match(r'missing fields')
 
 
 @mock.patch.dict(os.environ, {}, clear=True)