bpo-38839: Fix some unused functions in tests (GH-17189)

diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index abccf32..6a88454 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -765,6 +765,7 @@
         self.assertEqual(hash('spam'), hash(b'spam'))
         hash((0,1,2,3))
         def f(): pass
+        hash(f)
         self.assertRaises(TypeError, hash, [])
         self.assertRaises(TypeError, hash, {})
         # Bug 1536021: Allow hash to return long objects