diff --git a/product/ERP5/tests/testInventoryAPI.py b/product/ERP5/tests/testInventoryAPI.py
index b7060b4d5c96dbad973fce3645a9054f304eced6..815520509403b9240243b8346ee378fd170fa7bb 100644
--- a/product/ERP5/tests/testInventoryAPI.py
+++ b/product/ERP5/tests/testInventoryAPI.py
@@ -2061,9 +2061,9 @@ class TestInventoryDocument(InventoryAPITestCase):
       workflow_history = self.workflow_tool.getInfoFor(ob=new_inventory, 
           name='history', wf_id=workflow_id)
       workflow_error_message = str(workflow_history[-1]['error_message'])
-      self.assertTrue(
-          workflow_error_message.find('There is already an inventory')>=0,
-          workflow_error_message)
+      self.assertTrue(len(workflow_error_message))
+      self.assertTrue(len([x for x in workflow_error_message \
+          if x.find('There is already an inventory')]))
 
       # Add a case in order to check a bug when the other inventory at the
       # same date does not change stock values
@@ -2081,9 +2081,9 @@ class TestInventoryDocument(InventoryAPITestCase):
       workflow_history = self.workflow_tool.getInfoFor(ob=new_inventory, 
           name='history', wf_id=workflow_id)
       workflow_error_message = str(workflow_history[-1]['error_message'])
-      self.assertTrue(
-          workflow_error_message.find('There is already an inventory')>=0,
-          workflow_error_message)
+      self.assertTrue(len(workflow_error_message))
+      self.assertTrue(len([x for x in workflow_error_message \
+          if x.find('There is already an inventory')]))
     finally:
       # remove all property sheet we added to type informations
       ttool = self.getTypesTool()