> the list_dir() nested function is never called
Verifying that load_tests is called is the purpose of this test. In this case should_recurse is false in _find_tests() and os.listdir() is not invoked by this method.

This new patch does not use vfs and list_dir and uses subtests to also check that TestLoader.discover() does consider that a path refers to a package directory when it contains an '__init__.pyc' file and no '__init__.py' file, and vice-versa.