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

diff --git a/Lib/test/test_turtle.py b/Lib/test/test_turtle.py
index 39b3d96..46ff4a3 100644
--- a/Lib/test/test_turtle.py
+++ b/Lib/test/test_turtle.py
@@ -2,6 +2,7 @@
 import unittest
 from test import support
 from test.support import import_helper
+from test.support import os_helper
 
 
 turtle = import_helper.import_module('turtle')
@@ -52,10 +53,10 @@
 class TurtleConfigTest(unittest.TestCase):
 
     def get_cfg_file(self, cfg_str):
-        self.addCleanup(support.unlink, support.TESTFN)
-        with open(support.TESTFN, 'w') as f:
+        self.addCleanup(os_helper.unlink, os_helper.TESTFN)
+        with open(os_helper.TESTFN, 'w') as f:
             f.write(cfg_str)
-        return support.TESTFN
+        return os_helper.TESTFN
 
     def test_config_dict(self):