Fail hard if an unknown field is provided

simple_history/models.py

@@ -608,11 +608,8 @@ def diff_against(self, old_history, excluded_fields=None, included_fields=None):
         current_values = model_to_dict(self, fields=fields)
 
         for field in fields:
-            try:
-                old_value = old_values[field]
-                current_value = current_values[field]
-            except KeyError:
-                continue
+            old_value = old_values[field]
+            current_value = current_values[field]
 
             if old_value != current_value:
                 changes.append(ModelChange(field, old_value, current_value))

simple_history/tests/tests/test_models.py

@@ -687,6 +687,18 @@ def test_history_diff_with_included_fields(self):
         self.assertEqual(delta.changed_fields, ["question"])
         self.assertEqual(len(delta.changes), 1)
 
+    def test_history_with_unknown_field(self):
+        p = Poll.objects.create(question="what's up?", pub_date=today)
+        p.question = "what's up, man?"
+        p.save()
+        new_record, old_record = p.history.all()
+        with self.assertRaises(KeyError):
+            with self.assertNumQueries(0):
+                new_record.diff_against(old_record, included_fields=["unknown_field"])
+
+        with self.assertNumQueries(0):
+            new_record.diff_against(old_record, excluded_fields=["unknown_field"])
+
 
 class GetPrevRecordAndNextRecordTestCase(TestCase):
     def assertRecordsMatch(self, record_a, record_b):