Using a library that is a wrapper around an API, seems to work fine and I can connect to the api with my credentials.

Cue me, a responsible dev, wanting to use Dependency Inversion using the library's interfaces so that I can mock them easily in tests.

var test lib.IObjectManager = lib.ObjectManager{}

Error: Return type of method 'GetA' is A and should be 'B' according to the interface!
Error: Return type of method 'GetE' is *E and should be 'E' according to the interface!

Clearly nobody ever tried to use that interface :/