Add test files for each class

[MarkOates]

Problem

There is hardly any test coverage of the models. A good step forward would be to add test files for each class, with at least one basic test.

[MarkOates]

Probably should start by adding tests for Action::Transform classes

[MarkOates]

There is a dilemma where there is a lot of redundant testing between transform tests and action tests. For example, if you look at split_note_test.h and split_note_action_test.h they're essentially identical.