Add test for FileSystemDirectory.GetDirectory.
Add test for FileSystemDirectory.GetDirectory.

BluewireTechnologies/cassette,andrewdavey/cassette,honestegg/cassette,honestegg/cassette,damiensawyer/cassette,BluewireTechnologies/cassette,honestegg/cassette,damiensawyer/cassette,andrewdavey/cassette,damiensawyer/cassette,andrewdavey/cassette