I propose to start updating tests to use directly support.import_helper and support.os_helper. Hai: do you want to work on that? Maybe start by focusing on import_helper (but if you modify a test, check for also symbols imported from os_helper).

When you modify tests, I suggest to remove "from .import_helper import ..." and "from .os_helper import ..." in support/__init__.py and then run tests, to ensure that you updated all imports of the modified tests.

Try to not create giant PRs modifying 100+ files. For example, limit a PR to 20 test files.

When PR 20812 will be merged and import_helper and os_helper will no longer be imported  by support, "import test.support" done after "import unittest"  will only import 17 modules which is way better than the situation in April!