Tolerate that a rule does not produce any amount when output quantity can differ from input

git-svn-id: https://svn.erp5.org/repos/public/erp5/sandbox/amount_generator@38138 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/BusinessProcess.py

@@ -718,12 +718,13 @@ class BusinessProcess(Path, XMLObject):
         + movement.getCausalityList())
       result.append(movement)
 
-    # result can not be empty
-    if not result: raise ValueError("A Business Process can not erase amounts")
-
     if not explanation.getSpecialiseValue().getSameTotalQuantity():
       return result
 
+    # result can not be empty
+    if not result:
+      raise ValueError("A Business Process can not erase amounts")
+
     # Sort movement list and make sure the total is equal to total_quantity
     total_quantity = amount.getQuantity()
     current_quantity = 0

product/ERP5/tests/testBPMCore.py

@@ -83,9 +83,7 @@ class TestBPMMixin(ERP5TypeTestCase):
     business_process._edit(**kw)
     self.createTradeModelPath(business_process,
       reference='default_path',
-      trade_phase_value_list=('default/payment',
-                              'default/discount',
-                              'default/tax'),
+      trade_phase_value_list=('default/discount', 'default/tax'),
       trade_date='trade_phase/default/invoicing')
     kw = dict(business_process=business_process,
               trade_phase='default/accounting',