Fix: Check database errors properly.

  - Have sane testing of object states

mreg/tests.py

@@ -6,6 +6,8 @@
 from itertools import combinations
 from unittest import mock
 
+from copy import deepcopy
+
 from unittest import mock
 
 from django.db import DatabaseError
@@ -301,18 +303,27 @@ def setUp(self):
     @mock.patch('django.db.models.Model.save')
     def test_update_serialno_handles_database_error(self, mock_save):
         mock_save.side_effect = DatabaseError
+        zone_sample = deepcopy(self.zone_sample)
+
+        # This will raise a DatabaseError, which we will catch and ignore.
+        # During the course of this update provcess, the serial number will be 
+        # incremented and the updated_at timestamp will be updated.
         self.zone_sample.update_serialno(force=True)
-
+
+        # The save() method should have been called exactly once.
         mock_save.assert_called_once()
 
-        # Assert that the zone's serial number has not changed
-        self.assertEqual(self.zone_sample.serialno, self.zone_sample.serialno)
-
-        # Assert that updated is still False
-        self.assertEqual(self.zone_sample.updated, False)
-
-        # Assert that serialno_updated_at has not changed
-        self.assertEqual(self.zone_sample.serialno_updated_at, self.zone_sample.serialno_updated_at)
+        # The serial number will be incremented during the run, before we try to save
+        # the object. Checking this increment verifies that we are running through
+        # the code to get ready to save.
+        self.assertEqual(zone_sample.serialno + 1, self.zone_sample.serialno)
+
+        # Refetch the object from the database.
+        zone_sample_db = ForwardZone.objects.get(name='example.org')
+
+        # Check that the serial number in the database is the same as the one we originally had.
+        self.assertEqual(zone_sample.serialno, zone_sample_db.serialno)
+        self.assertEqual(zone_sample.serialno_updated_at, zone_sample_db.serialno_updated_at)
 
     def test_model_can_create_ns(self):
         """Test that the model is able to create an Ns."""