try to make this message more self explanatory

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@44190 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/mixin/movement_collection_updater.py

@@ -73,7 +73,9 @@ class MovementCollectionUpdaterMixin:
     # Get divergence testers
     tester_list = self._getMatchingTesterList()
     if not tester_list and len(prevision_movement_list) > 1:
-      raise ValueError("It is not possible to match movements without divergence testers")
+      raise ValueError("It is not possible to match movements from movement"
+          " collection updater %r, because it does not contain any tester"
+          " configured as matching provider" % (self, ))
 
     # Create small groups of movements per hash keys
     decision_movement_dict = {}