It would be very useful if you pointed that out. To me the question seemed like someone new coming from the ruby world looking ways on how to do things in elixir. A short sentence including the fact that you are aware of how DI is done in functional languages and mocking tools would save us a lot of time.
Generally speaking if the solutions provided by me and @LostKobrakai are a no-go, then you are out of luck, unless you fancy doing some metaprogramming. I personally cannot see how provided solutions are in any way worse than the one you pointed, but I am not interested in arguing on that as it goes into off-topic.
