tests(config): use sentinel exception to avoid masking real errors on rollback

Replace bare 'except IntegrityError: pass' with a ForceRollback sentinel
exception and self.assertRaises so that only the deliberate rollback is caught;
this prevents real IntegrityErrors raised by devicegroup_templates_change_handler
or mock_delay assertions from being silently swallowed.

Author: prakash-kalwaniya

openwisp_controller/config/tests/test_handlers_transaction.py

@@ -1,6 +1,6 @@
 from unittest.mock import patch
 
-from django.db import IntegrityError, transaction
+from django.db import transaction
 from django.test import TransactionTestCase
 from swapper import load_model
 
@@ -11,6 +11,10 @@
 Config = load_model("config", "Config")
 
 
+class ForceRollback(Exception):
+    """Sentinel exception used to deliberately roll back a transaction in tests."""
+
+
 class TestHandlersTransaction(TransactionTestCase):
     @patch("openwisp_controller.config.tasks.change_devices_templates.delay")
     def test_devicegroup_templates_change_handler_on_commit(self, mock_delay):
@@ -65,13 +69,11 @@ def __init__(self, id, model_name):
 
                 # Case 2: Transaction rolls back
                 mock_delay.reset_mock()
-                try:
+                with self.assertRaises(ForceRollback):
                     with transaction.atomic():
                         devicegroup_templates_change_handler(mock_instance, **kwargs)
                         mock_delay.assert_not_called()
-                        raise IntegrityError("Force rollback")
-                except IntegrityError:
-                    pass
+                        raise ForceRollback
 
                 # Should not be called because it rolled back
                 mock_delay.assert_not_called()
@@ -97,13 +99,11 @@ def test_devicegroup_templates_change_handler_list_branch(self, mock_delay):
 
         with self.subTest("list branch: delay not called on rollback"):
             mock_delay.reset_mock()
-            try:
+            with self.assertRaises(ForceRollback):
                 with transaction.atomic():
                     devicegroup_templates_change_handler(instance_list, **kwargs)
                     mock_delay.assert_not_called()
-                    raise IntegrityError("Force rollback")
-            except IntegrityError:
-                pass
+                    raise ForceRollback
 
             # Should not be called because it rolled back
             mock_delay.assert_not_called()