[1.11.x] Fixed #28293 -- Fixed union(), intersection(), and difference() when combining with an EmptyQuerySet.

Thanks Jon Dufresne for the report and Tim Graham for the review.

Backport of 82175ead723f8fa3f9271fbd4b24275097029aab from master

1 files changed, 25 insertions, 0 deletions

diff --git a/tests/queries/test_qs_combinators.py b/tests/queries/test_qs_combinators.py
index a0faab2eb7..ec341952ea 100644
--- a/tests/queries/test_qs_combinators.py
+++ b/tests/queries/test_qs_combinators.py
@@ -45,6 +45,31 @@ class QuerySetSetOperationTests(TestCase):
         self.assertEqual(len(list(qs1.union(qs2, all=True))), 20)
         self.assertEqual(len(list(qs1.union(qs2))), 10)
 
+    @skipUnlessDBFeature('supports_select_intersection')
+    def test_intersection_with_empty_qs(self):
+        qs1 = Number.objects.all()
+        qs2 = Number.objects.none()
+        self.assertEqual(len(qs1.intersection(qs2)), 0)
+        self.assertEqual(len(qs2.intersection(qs1)), 0)
+        self.assertEqual(len(qs2.intersection(qs2)), 0)
+
+    @skipUnlessDBFeature('supports_select_difference')
+    def test_difference_with_empty_qs(self):
+        qs1 = Number.objects.all()
+        qs2 = Number.objects.none()
+        self.assertEqual(len(qs1.difference(qs2)), 10)
+        self.assertEqual(len(qs2.difference(qs1)), 0)
+        self.assertEqual(len(qs2.difference(qs2)), 0)
+
+    def test_union_with_empty_qs(self):
+        qs1 = Number.objects.all()
+        qs2 = Number.objects.none()
+        self.assertEqual(len(qs1.union(qs2)), 10)
+        self.assertEqual(len(qs2.union(qs1)), 10)
+        self.assertEqual(len(qs2.union(qs1, qs1, qs1)), 10)
+        self.assertEqual(len(qs2.union(qs1, qs1, all=True)), 20)
+        self.assertEqual(len(qs2.union(qs2)), 0)
+
     def test_union_bad_kwarg(self):
         qs1 = Number.objects.all()
         msg = "union() received an unexpected keyword argument 'bad'"