Yes, but with every large applications I've been bitten by non-functional problems in production with major Java migrations, as non-functional testing is usuall

Yes, but with every large applications I've been bitten by non-functional problems in production with major Java migrations, as non-functional testing is usually not as extensive as user testing. The answer was to: "So better start today making sure it runs on Java 10. It doesn't need to be deployed straight into production." Making sure it runs on Java 10 is not the problem, I expressed myself too fuzzy.