I did see this comment (continuing the discussion from email...), but thought you might have more coming here, since it's only part of what I suggested.  The point of switching to a fixture for the legacy formatter is to be able to have it actually print to a `StringIO` the output of the formatter, and then you can set expectations about what it outputs.  This will make the tests more focused on behavior (e.g. the resulting output of a particular formatter) and less on the implementation (e.g. which specific methods get called) -- which will come in handy when it comes time to refactor.

Are you planning on moving in that direction?