Add unit test for issue #14 - already passes.
Add unit test for issue #14 - already passes.

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