do not define a new date if a date is already defined

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@14030 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Banking/tests/TestERP5BankingMixin.py

@@ -693,7 +693,8 @@ class TestERP5BankingMixin:
     Compute and set the source reference for a document
     """
     # document must have a date defined
-    doc.edit(start_date=DateTime())
+    if doc.getStartDate() is None:
+      doc.edit(start_date=DateTime())
     # call script to set source reference
     doc.Baobab_getUniqueReference()