test_dictviews: Add testcase for dictviews_sub (GH-16660)

Author: corona10

Lib/test/test_dictviews.py

@@ -219,11 +219,13 @@ def test_set_operations_with_iterator(self):
         self.assertEqual(origin.keys() & iter([1, 2]), {1})
         self.assertEqual(origin.keys() | iter([1, 2]), {1, 2, 3})
         self.assertEqual(origin.keys() ^ iter([1, 2]), {2, 3})
+        self.assertEqual(origin.keys() - iter([1, 2]), {3})
 
         items = origin.items()
         self.assertEqual(items & iter([(1, 2)]), {(1, 2)})
         self.assertEqual(items ^ iter([(1, 2)]), {(3, 4)})
         self.assertEqual(items | iter([(1, 2)]), {(1, 2), (3, 4)})
+        self.assertEqual(items - iter([(1, 2)]), {(3, 4)})
 
     def test_recursive_repr(self):
         d = {}