Tested Model.set_FOO_order() with an unrelated object.

tests/order_with_respect_to/base_tests.py

@@ -50,6 +50,13 @@ class BaseOrderWithRespectToTests:
         a2 = self.Answer.objects.create(text="Number five", question=self.q1)
         self.assertEqual(list(a1.question.get_answer_order()), list(a2.question.get_answer_order()))
 
+    def test_set_order_unrelated_object(self):
+        """An answer that's not related isn't updated."""
+        q = self.Question.objects.create(text='other')
+        a = self.Answer.objects.create(text='Number five', question=q)
+        self.q1.set_answer_order([o.pk for o in self.q1.answer_set.all()] + [a.pk])
+        self.assertEqual(self.Answer.objects.get(pk=a.pk)._order, 0)
+
     def test_change_ordering(self):
         # The ordering can be altered
         a = self.Answer.objects.create(text="Number five", question=self.q1)