bpo-40275: Use new test.support helper submodules in tests (GH-21449)

diff --git a/Lib/test/test_mmap.py b/Lib/test/test_mmap.py
index 5400f25..8f34c18 100644
--- a/Lib/test/test_mmap.py
+++ b/Lib/test/test_mmap.py
@@ -1,5 +1,6 @@
-from test.support import (TESTFN, import_module, unlink,
-                          requires, _2G, _4G, gc_collect, cpython_only)
+from test.support import (requires, _2G, _4G, gc_collect, cpython_only)
+from test.support.import_helper import import_module
+from test.support.os_helper import TESTFN, unlink
 import unittest
 import os
 import re