adds simple unit tests

hi jason:

thanks for the nice module. i saw some comments in the source about adding custom policy generation in the module -- i'd love to help out! (my use case is restricting to `ipAddress`).

first things first, wanted to check with you about adding some _very_ simple tests to existing api so that i don't cause any unwanted breakage (as i tend do do :-1:).

this pull request just does some super-simple assertions on the existing functionality. with that in place, then i'd be happy to continue branching off for custom policy gen.

let me know what you think!