Browser testing with external front end and api servers

I have an elixir phoenix project which powers my API and another pure elixir project which is my test suite for the entire platform.
This test suite lives alongside the front end code (which is a react project and has its own server started using ‘yarn start’).

I want to keep this separation of concerns as my API is likely to be broken up into smaller services but the front end will always span across services, so it seems the logical place for the end to end tests driving the browser.

So, I am using ExUnit and hound to build my test suite, but I am struggling to work out how to automatically start the external processes at the start and stop them at the end.

Can anyone help me work this out ? I want a completely automated test suite so I dont want to be starting processes manually before hand.