Add an integration test that uses the enforce module to enforce types

[oadams]

https://github.com/RussBaz/enforce

Low priority but could be worth doing at some point.

[shuttle1987]

Agree with the priority being low, perhaps we can make a low-priority issue tag for such matters. It could be good however to add this into the CI pipeline, as some subtle typing bugs can slip through that this would catch.

[oadams]

Using it in Travis testing sounds like a good idea!