skip union tests on transactions

Author: timgraham

django_mongodb_backend/features.py

@@ -589,3 +589,8 @@ def supports_atlas_search(self):
             return False
         else:
             return True
+
+    @cached_property
+    def supports_select_union(self):
+        # Stage not supported inside of a multi-document transaction: $unionWith
+        return not self.supports_transactions

tests/queries_/test_objectid.py

@@ -1,6 +1,6 @@
 from bson import ObjectId
 from django.core.exceptions import ValidationError
-from django.test import TestCase
+from django.test import TestCase, skipUnlessDBFeature
 
 from .models import Order, OrderItem, Tag
 
@@ -75,13 +75,15 @@ def test_filter_parent_by_children_values_obj(self):
         parent_qs = Tag.objects.filter(children__id__in=child_ids).distinct().order_by("name")
         self.assertSequenceEqual(parent_qs, [self.t1])
 
+    @skipUnlessDBFeature("supports_select_union")
     def test_filter_group_id_union_with_str(self):
         """Combine queries using union with string values."""
         qs_a = Tag.objects.filter(group_id=self.group_id_str_1)
         qs_b = Tag.objects.filter(group_id=self.group_id_str_2)
         union_qs = qs_a.union(qs_b).order_by("name")
         self.assertSequenceEqual(union_qs, [self.t3, self.t4])
 
+    @skipUnlessDBFeature("supports_select_union")
     def test_filter_group_id_union_with_obj(self):
         """Combine queries using union with ObjectId values."""
         qs_a = Tag.objects.filter(group_id=self.group_id_obj_1)