#18 add tests

While I've been doing ad-hoc "looks okay to me"-style tests, this has been letting bugs through that should have been caught. We should add some unit tests where we can, and once #17 is fixed, integration tests, both native and in shadow.

Progress on this in 56b839b46c.

Further progress in 9d63492f83 (already caught one bug: af685e6c7c).

Calling this fixed with ba77863115.