start using correct model in tests

tests/factories/site.py

@@ -0,0 +1,25 @@
+import factory
+from django.utils.text import slugify
+from wagtail.wagtailcore.models import Site
+from wagtail_factories.factories import MP_NodeFactory
+
+from tests.sandbox.pages.models import HomePage
+
+
+class PageFactory(MP_NodeFactory):
+    title = 'Test page'
+    slug = factory.LazyAttribute(lambda obj: slugify(obj.title))
+
+    class Meta:
+        model = HomePage
+
+
+class SiteFactory(factory.DjangoModelFactory):
+    hostname = 'localhost'
+    port = factory.Sequence(lambda n: 81 + n)
+    site_name = 'Test site'
+    root_page = factory.SubFactory(PageFactory, parent=None)
+    is_default_site = False
+
+    class Meta:
+        model = Site