Add a comment about not using assertTrue

Change-Id: I21be4f96a1a12ace1d579d50a2cd91e0fa899fb6

keystone/tests/unit/identity/test_core.py

@@ -198,6 +198,9 @@ class TestShadowUsers(unit.TestCase):
         self.assertIsNotNone(user['name'])
         self.assertIsNone(user['password_expires_at'])
         self.assertIsNone(user['domain_id'])
+        # NOTE(breton): below, attribute `enabled` is explicitly tested to be
+        # equal True. assertTrue should not be used, because it converts
+        # the passed value to bool().
         self.assertEqual(True, user['enabled'])
 
     def test_shadow_existing_federated_user(self):