@@ -211,13 +211,9 @@ def old_get_auth(sock, dname, host, dno):
             if len(parts) == 3:
                 auth_name = parts[1]
                 hexauth = parts[2]
-                auth = b''
 
                 # Translate hexcode into binary
-                for i in range(0, len(hexauth), 2):
-                    auth = auth + chr(int(hexauth[i:i+2], 16))
-
-                auth_data = auth
+                auth_data = bytes.fromhex(hexauth)
     except os.error:
         pass
 
 
@@ -2,6 +2,7 @@
 
 from functools import partial
 import gc
+import io
 import socket
 import sys
 import unittest
@@ -152,6 +153,15 @@ def ensure_not_inheritable(*args):
                     expected_calls.append(('ensure_not_inheritable', s))
                 self.assertEqual(calls, expected_calls)
 
+    def test_old_get_auth(self):
+        for xauth_output, expected in (
+            ('host/unix:0  MIT-MAGIC-COOKIE-1  0123abcd\n', ('MIT-MAGIC-COOKIE-1', b'\x01\x23\xab\xcd')),
+            # No cookie for this display.
+            ('', ('', b'')),
+        ):
+            with patch('os.popen', return_value=io.StringIO(xauth_output)):
+                self.assertEqual(unix_connect.old_get_auth(None, 'host/unix:0', 'host', 0), expected)
+
     def test_leaking_sockets(self):
         with warnings.catch_warnings():
             warnings.simplefilter("error", ResourceWarning)