you don’t need it because you have great testing tools in Ecto and phoenix. Those, in someway, are core libraries. If you haven’t read Mocks and explicit contracts is really interesting and talks about it.
But sorry, I didn’t want to move the thread to the decoupling and testing topic sorry 
UPDATE: I inherited some python microservices (in production) which were using directly AWS S3 calls all over the place. When we had to move some part of the storage locally, it was a nightmare to migrate. If we had a wrapper around it we would have saved days…
