My thought was to have the tests assert things through `#display_type`. This way the internals of the private methods of the class could change but we have a way of testing the result through the high-level behavior.

It's probably not 100% ideal but it gives us coverage so we can refactor later if need be.  I could be swayed to spend some time to write some unit tests for the private methods (although I think it would be largely duplicating the higher-level tests).