To answer your first question: Inspect is an Elixir protocol that is implemented for some of your schema modules. Most likely because you have redact: true set on some fields. Ecto derives a custom Inspect implementation in that case.
In general: for each protocol Proto that is implemented for a module Mod, there will be an implementation module called Proto.Mod.
As for testing or excluding the modules, maybe somebody else has a recommendation. (I‘m not tracking test coverage in any of my projects) You could write tests that check if the schema fields are redacted when inspected - at that point you’d be testing Ecto itself though 
