[#3872] OrderFactory breaks if settings.SITE_ID isn't set

src/oscar/test/factories/order.py

 
 import factory
 from django.conf import settings
+from django.contrib.sites.models import Site
 
 from oscar.core.loading import get_class, get_model
 from oscar.core.utils import slugify
     if hasattr(settings, 'OSCAR_INITIAL_ORDER_STATUS'):
         status = settings.OSCAR_INITIAL_ORDER_STATUS
 
-    site_id = settings.SITE_ID
+    site_id = factory.LazyAttribute(
+        lambda o: settings.SITE_ID if hasattr(settings, "SITE_ID") else Site.objects.first()
+    )
     number = factory.LazyAttribute(lambda o: '%d' % (100000 + o.basket.pk))
     basket = factory.SubFactory(
         'oscar.test.factories.BasketFactory')