bpo-40275: Use new test.support helper submodules in tests (GH-21219)

diff --git a/Lib/test/test_regrtest.py b/Lib/test/test_regrtest.py
index 6745be6..39af0d9 100644
--- a/Lib/test/test_regrtest.py
+++ b/Lib/test/test_regrtest.py
@@ -18,6 +18,7 @@
 import unittest
 from test import libregrtest
 from test import support
+from test.support import os_helper
 from test.libregrtest import utils
 
 
@@ -161,12 +162,12 @@
                 self.assertEqual(ns.ignore_tests, ['pattern'])
                 self.checkError([opt], 'expected one argument')
 
-        self.addCleanup(support.unlink, support.TESTFN)
-        with open(support.TESTFN, "w") as fp:
+        self.addCleanup(os_helper.unlink, os_helper.TESTFN)
+        with open(os_helper.TESTFN, "w") as fp:
             print('matchfile1', file=fp)
             print('matchfile2', file=fp)
 
-        filename = os.path.abspath(support.TESTFN)
+        filename = os.path.abspath(os_helper.TESTFN)
         ns = libregrtest._parse_args(['-m', 'match',
                                       '--ignorefile', filename])
         self.assertEqual(ns.ignore_tests,
@@ -183,12 +184,12 @@
                                       '-m', 'pattern2'])
         self.assertEqual(ns.match_tests, ['pattern1', 'pattern2'])
 
-        self.addCleanup(support.unlink, support.TESTFN)
-        with open(support.TESTFN, "w") as fp:
+        self.addCleanup(os_helper.unlink, os_helper.TESTFN)
+        with open(os_helper.TESTFN, "w") as fp:
             print('matchfile1', file=fp)
             print('matchfile2', file=fp)
 
-        filename = os.path.abspath(support.TESTFN)
+        filename = os.path.abspath(os_helper.TESTFN)
         ns = libregrtest._parse_args(['-m', 'match',
                                       '--matchfile', filename])
         self.assertEqual(ns.match_tests,
@@ -237,7 +238,7 @@
 
     def test_testdir(self):
         ns = libregrtest._parse_args(['--testdir', 'foo'])
-        self.assertEqual(ns.testdir, os.path.join(support.SAVEDCWD, 'foo'))
+        self.assertEqual(ns.testdir, os.path.join(os_helper.SAVEDCWD, 'foo'))
         self.checkError(['--testdir'], 'expected one argument')
 
     def test_runleaks(self):
@@ -284,7 +285,7 @@
             with self.subTest(opt=opt):
                 ns = libregrtest._parse_args([opt, 'foo'])
                 self.assertEqual(ns.coverdir,
-                                 os.path.join(support.SAVEDCWD, 'foo'))
+                                 os.path.join(os_helper.SAVEDCWD, 'foo'))
                 self.checkError([opt], 'expected one argument')
 
     def test_nocoverdir(self):
@@ -363,7 +364,7 @@
         self.testdir = os.path.realpath(os.path.dirname(__file__))
 
         self.tmptestdir = tempfile.mkdtemp()
-        self.addCleanup(support.rmtree, self.tmptestdir)
+        self.addCleanup(os_helper.rmtree, self.tmptestdir)
 
     def create_test(self, name=None, code=None):
         if not name:
@@ -384,7 +385,7 @@
         name = self.TESTNAME_PREFIX + name
         path = os.path.join(self.tmptestdir, name + '.py')
 
-        self.addCleanup(support.unlink, path)
+        self.addCleanup(os_helper.unlink, path)
         # Use 'x' mode to ensure that we do not override existing tests
         try:
             with open(path, 'x', encoding='utf-8') as fp:
@@ -770,8 +771,8 @@
         # Write the list of files using a format similar to regrtest output:
         # [1/2] test_1
         # [2/2] test_2
-        filename = support.TESTFN
-        self.addCleanup(support.unlink, filename)
+        filename = os_helper.TESTFN
+        self.addCleanup(os_helper.unlink, filename)
 
         # test format '0:00:00 [2/7] test_opcodes -- test_grammar took 0 sec'
         with open(filename, "w") as fp:
@@ -886,7 +887,7 @@
         test = self.create_test('huntrleaks', code=code)
 
         filename = 'reflog.txt'
-        self.addCleanup(support.unlink, filename)
+        self.addCleanup(os_helper.unlink, filename)
         output = self.run_tests('--huntrleaks', '3:3:', test,
                                 exitcode=2,
                                 stderr=subprocess.STDOUT)
@@ -997,8 +998,8 @@
         testname = self.create_test(code=code)
 
         # only run a subset
-        filename = support.TESTFN
-        self.addCleanup(support.unlink, filename)
+        filename = os_helper.TESTFN
+        self.addCleanup(os_helper.unlink, filename)
 
         subset = [
             # only ignore the method name
@@ -1038,8 +1039,8 @@
         self.assertEqual(methods, all_methods)
 
         # only run a subset
-        filename = support.TESTFN
-        self.addCleanup(support.unlink, filename)
+        filename = os_helper.TESTFN
+        self.addCleanup(os_helper.unlink, filename)
 
         subset = [
             # only match the method name