3 years later! spotted this post while dealing with some legacy code.
If you really need to restart a process that’s part of the app sup tree, say in the setup block of your test, you can do that with:
:ok = Supervisor.terminate_child(My.Supervisor, My.Pipe)
{:ok, _} = Supervisor.restart_child(My.Supervisor, My.Pipe)
And in order to make it work you’d need to name your Supervisor in the application start, like:
Supervisor.start_link(children, name: My.Supervisor)
Note: restarting child would use original child spec defined in your app. So if you’d like to override some options passed into a supervised module you’d need to not rely on actual options in the child spec, but on the configuration of your supervised module that’s pulled from the app configs. In the original example that topic started brought up that My.Pipe is getting started with empty options.
I saw that approach recommended by @sasajuric a while back and I would suggest you do that only if you have no other way and you just need to get things done quick. Of course, most likely you wouldn’t like to have such test running async.
But the approach with start_supervised that @LostKobrakai and @idi527 pointed out above is what is probably an ideal way of doing things 