Video:
https://www.youtube.com/watch?v=hYCUy-9yq_M
Quite a bit of theory and a bit of practice about how you can use UI tests to give yourself a framework to improve an existing, untested app without unintentionally breaking functionality for your users.
Video of XCUI tests running painfully slowly available here: https://youtu.be/XbqDFokGkQc