Ecto timeout errors when wrapping into cachex calls in tests

I might have found the reason why it works when not using Cachex. Cachex spawns its own process, and the fallback function for querying the database gets executed in the context of the cachex process. And this process has no access to the database connection. Is this assumption right? If yes, how do I fix that w/o calling Ecto.Adapters.SQL.Sandbox.allow?