Run PHPUnit tests automatically on file change on OSX / Mac

I shared this technique for Linux already : https://www.youtube.com/watch?v=pvzxp0VXnC4&t=3s I got asked a bunch of times how to do this for OSX. So here we go, this is how to run a command - in this case, our PHPUnit tests - whenever we change any `.php` file in our project. The command to install `fswatch` on OSX is `brew install fswatch`.