Regarding upgrades, theoretically, this should be handled by the
regression testing built into Cloud Manager. Essentially it will build a
copy of the App + AEM Feature Model and run regression tests against
that, but frankly I'm concerned as well as IMO the issues you find in
upgrades usually aren't discoverable via compilation or testing. This is
one of the questions I posed to Cedric Huesler on Twitter:
https://twitter.com/KlcoDanR/status/1217063177810214912