Add unit tests for types

We should find some way to unit test some of our more complex types, to ensure they're guaranteeing exactly what we think they are. In particular, the types used by the Base Controller (and soon the controller messaging system) are fairly complex and deserve additional validation.

Start by locating the complex types used by the Base Controller and reviewing the repository's existing unit-test setup. Determine which guarantees need validation, including types relevant to the controller messaging system, and consider the work done when those guarantees are covered by focused unit tests.

Written by the indexing model from the issue text.