It took me a bit to figure this all out, and I’d love to hear from others on how they test their custom tasks.
Heeey! Thanks for the heads up in this! This helped me to fix my problem with a mix task test that was hiding mix messages from other apps in the same umbrella. Here is the topic I opened for the problem.
As you can see, I used Mix.shell(Mix.Shell.Process) and had problems with the umbrella apps logs. Here is the code I used to fix it:
setup do
Mix.shell(Mix.Shell.Process)
on_exit fn ->
Mix.shell(Mix.Shell.IO)
end
:ok
end
If you could update your post with it, I guess it can be a very common problem for other people who like to make their own mix tasks. 
