Added tests for already fixed #20101

The ticket dealt with a case where one query had .exclude() that
produced a subquery, the other query had a join to the same model that
was subqueried in the first query. This was already fixed in master, so
only test added.

tests/queries/tests.py

@@ -2808,3 +2808,19 @@ class RelabelCloneTest(TestCase):
         # not change results for the parents query.
         self.assertEqual(list(children), [my2])
         self.assertEqual(list(parents), [my1])
+
+class Ticket20101Tests(TestCase):
+    def test_ticket_20101(self):
+        """
+        Tests QuerySet ORed combining in exclude subquery case.
+        """
+        t = Tag.objects.create(name='foo')
+        a1 = Annotation.objects.create(tag=t, name='a1')
+        a2 = Annotation.objects.create(tag=t, name='a2')
+        a3 = Annotation.objects.create(tag=t, name='a3')
+        n = Note.objects.create(note='foo', misc='bar')
+        qs1 = Note.objects.exclude(annotation__in=[a1, a2])
+        qs2 = Note.objects.filter(annotation__in=[a3])
+        self.assertTrue(n in qs1)
+        self.assertFalse(n in qs2)
+        self.assertTrue(n in (qs1 | qs2))