bpo-40275: Use new test.support helper submodules in tests (GH-21743)

diff --git a/Lib/test/test_urllib2net.py b/Lib/test/test_urllib2net.py
index cb74685..c1d55ee 100644
--- a/Lib/test/test_urllib2net.py
+++ b/Lib/test/test_urllib2net.py
@@ -1,6 +1,7 @@
 import errno
 import unittest
 from test import support
+from test.support import os_helper
 from test.support import socket_helper
 from test.test_urllib2 import sanepathname2url
 
@@ -148,7 +149,7 @@
         self._test_urls(urls, self._extra_handlers())
 
     def test_file(self):
-        TESTFN = support.TESTFN
+        TESTFN = os_helper.TESTFN
         f = open(TESTFN, 'w')
         try:
             f.write('hi there\n')