Helper and docs for offlinesales API (#5302)

src/tests/base/test_cross_selling.py

@@ -28,10 +28,10 @@ import pytest
 from django.utils.timezone import now
 from django_scopes import scopes_disabled
 from freezegun import freeze_time
-from tests import assert_num_queries
 
 from pretix.base.models import CartPosition, Discount, Event, Organizer
 from pretix.base.services.cross_selling import CrossSellingService
+from pretix.testutils.queries import assert_num_queries
 
 
 @pytest.fixture