diff --git a/ming/tests/test_session.py b/ming/tests/test_session.py
index 9e2e3b9..80fe412 100644
--- a/ming/tests/test_session.py
+++ b/ming/tests/test_session.py
@@ -81,9 +81,9 @@ def test_base_session(self):
         doc = self.TestDocNoSchema({'_id':5, 'a':5})
         sess.save(doc)
         impl.save.assert_called_with(dict(_id=5, a=5))
-        # doc = self.TestDocNoSchema({'_id':5, 'a':5})
-        # sess.save(doc, 'a')
-        # impl.update.assert_called_with(dict(_id=5), {'$set':dict(a=5)})
+        doc = self.TestDocNoSchema({'_id':5, 'a':5, 'b': 6})
+        sess.save(doc, 'a')
+        impl.update.assert_called_with(dict(_id=5), {'$set':dict(a=5)})
         doc = self.TestDocNoSchema({'_id':5, 'a':5})
         impl.insert.return_value = bson.ObjectId()
         sess.insert(doc)