If you are designing a loglang, then you will probably need to read up
about diathesis, semantic roles v. grammatical roles, and decide which
precise meaning you give 'middle'. But if, as I suspect, you are
designing an artlang, then my advice would be to model your middle voice
on the behavior of reflexive verbs in languages like French, Spanish or
Italian and not worry about 'tests'.
Hope this helps.