Restore UnsealedAttributeAccess elevation to error in tests.

Author: charettes

tests/test_query.py

@@ -1,4 +1,5 @@
 import pickle
+import warnings
 
 from django.apps import apps
 from django.contrib.contenttypes.models import ContentType
@@ -49,6 +50,10 @@ def setUpTestData(cls):
         tests_models = tuple(apps.get_app_config("tests").get_models())
         ContentType.objects.get_for_models(*tests_models, for_concrete_models=True)
 
+    def setUp(self):
+        warnings.filterwarnings("error", category=UnsealedAttributeAccess)
+        self.addCleanup(warnings.resetwarnings)
+
     def test_state_sealed_assigned(self):
         instance = SeaLion.objects.seal().get()
         self.assertTrue(instance._state.sealed)