How to run callback with jest --watch

I started to learn ReactJS yesterday (to be used in my next product), I am willing to set up my dev environment but now I'm stuck with Jest...

Having a bluetooth lightbulb on my desk (already op with scripts etc..), I want to get a red light when my tests launched with jest --watch fail (see create-react-app from FB devs here) The problem is, I don't know how to run a callback after the tests, it seems like no one ran into this issue on the interwebz, no solution found yet for me.

Thanks for your help