Safeguarding From Deprecation Regressions During an Upgrade

You are upgrading a Rails application. You finished fixing a deprecation warning and it’s not present anymore. You continue working on other tasks and one day you find out the deprecation is back in the codebase. New code was added using the deprecated behavior, but it was not detected and now it needs to be fixed again…How can you prevent that from happening and, at the same time, let the team know?.