Add tests for mixed base64 alphabets

Author: matthieucan

Lib/test/test_email/test__encoded_words.py

@@ -43,6 +43,9 @@ def test_urlsafe_alphabet(self):
           b'QW5tZWxkdW5nIE5ldHphbnNjaGx1c3MgU_xkcmluZzNwLmpwZw==',
           b'Anmeldung Netzanschluss S\xfcdring3p.jpg',
           [errors.InvalidBase64CharactersDefect])
+        # Mix of 2 base64 alphabets
+        self._test(b'aGVsbG8_Pz8/', b'hello????', [errors.InvalidBase64CharactersDefect])
+
 
     def test_invalid_character(self):
         self._test(b'dm\x01k===', b'vi', [errors.InvalidBase64CharactersDefect])

Lib/test/test_email/test_email.py

@@ -4666,6 +4666,8 @@ def test_decode(self):
         eq(base64mime.decode(
            'QW5tZWxkdW5nIE5ldHphbnNjaGx1c3MgU_xkcmluZzNwLmpwZw=='),
            b'Anmeldung Netzanschluss S\xfcdring3p.jpg')
+        # Mix of 2 base64 alphabets
+        eq(base64mime.decode('aGVsbG8_Pz8/'), b'hello????')
 
     def test_encode(self):
         eq = self.assertEqual