diff --git a/csst_common/data_manager.py b/csst_common/data_manager.py
index b98ac0c73140cbe7c7e2cc730281c0b46cb4a8d2..7591f0574c547bdae255b7231b393d3bf67a0be3 100644
--- a/csst_common/data_manager.py
+++ b/csst_common/data_manager.py
@@ -274,7 +274,8 @@ class CsstMbiDataManager:
         return fp
 
     @staticmethod
-    def __testddl__(self):
+    def __testddl__():
+        """ test function """
         dm = CsstMbiDataManager(
             ver_sim="C5.2",
             dir_l0="/nfsdata/share/csst_simulation_data/Cycle-5-SimuData/multipleBandsImaging"