bpo-40275: Use new test.support helper submodules in tests (GH-21314)

diff --git a/Lib/test/test_fileio.py b/Lib/test/test_fileio.py
index 26e4500..ff611a9 100644
--- a/Lib/test/test_fileio.py
+++ b/Lib/test/test_fileio.py
@@ -9,8 +9,9 @@
 from weakref import proxy
 from functools import wraps
 
-from test.support import (TESTFN, TESTFN_UNICODE, check_warnings, run_unittest,
-                          make_bad_fd, cpython_only, swap_attr)
+from test.support import (run_unittest, cpython_only, swap_attr)
+from test.support.os_helper import (TESTFN, TESTFN_UNICODE, make_bad_fd)
+from test.support.warnings_helper import check_warnings
 from collections import UserList
 
 import _io  # C implementation of io