1 files changed, 30 insertions, 1 deletions
diff --git a/tests/model_formsets/tests.py b/tests/model_formsets/tests.py
index 40f206277b..9436642573 100644
--- a/tests/model_formsets/tests.py
+++ b/tests/model_formsets/tests.py
@@ -1782,7 +1782,36 @@ class ModelFormsetTest(TestCase):
         formset = ProductFormSet()
 
         queryset = formset.get_queryset()
-        self.assertEqual(queryset.query.order_by, ("id",))
+        self.assertEqual(queryset.query.order_by, ("pk",))
+
+    def test_get_queryset_appends_pk_to_explicit_queryset_ordering(self):
+        # Author.name is non-unique, so order_by("name") is not totally
+        # ordered.
+        AuthorFormSet = modelformset_factory(Author, fields="__all__")
+        formset = AuthorFormSet(queryset=Author.objects.order_by("name"))
+
+        queryset = formset.get_queryset()
+        self.assertEqual(queryset.query.order_by, ("name", "pk"))
+
+    def test_get_queryset_appends_pk_to_meta_ordering(self):
+        # Author has Meta.ordering = ("name",) which is not deterministic
+        # by itself.
+        AuthorFormSet = modelformset_factory(Author, fields="__all__")
+        formset = AuthorFormSet()
+
+        queryset = formset.get_queryset()
+        self.assertEqual(queryset.query.order_by, ("name", "pk"))
+
+    def test_get_queryset_unchanged_when_already_totally_ordered(self):
+        # Ordering by pk is already totally ordered; pk must not be
+        # appended again.
+        AuthorFormSet = modelformset_factory(Author, fields="__all__")
+        formset = AuthorFormSet(queryset=Author.objects.order_by("pk"))
+
+        queryset = formset.get_queryset()
+        # Must be exactly ("pk",), not ("pk", "pk").
+        self.assertEqual(queryset.query.order_by, ("pk",))
+        self.assertIs(queryset.totally_ordered, True)
 
     def test_prevent_duplicates_from_with_the_same_formset(self):
         FormSet = modelformset_factory(Product, fields="__all__", extra=2)