Improve test converage for Asset.
Improve test converage for Asset.

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