Index: Lib/test/test_mimetypes.py
===================================================================
--- Lib/test/test_mimetypes.py	(revisão 86582)
+++ Lib/test/test_mimetypes.py	(cópia de trabalho)
@@ -61,6 +61,14 @@
         # And now for no hits
         all = self.db.guess_all_extensions('image/jpg', strict=True)
         eq(all, [])
+    
+    def test_guess_extension_all_types(self):
+        eq = self.assertEqual
+        unless = self.assertTrue
+        all_with_exts = set(self.db.guess_extension('text/plain', all_exts=True))
+        all_without_exts = self.db.guess_extension('not_exits_type', all_exts=True)
+        unless(all_with_exts >= set(('.bat', '.c', '.h', '.ksh', '.pl', '.txt')))
+        eq(all_without_exts, (None,))
 
 
 @unittest.skipUnless(sys.platform.startswith("win"), "Windows only")