Should I be worried about this strange notification from Delta? I got a notification from the Fly Delta app that just says "test". The icon appears to be missing. Should I be concerned about this? I've uninstalled the Delta app, but I'm unsure if I need to do more.

This is, to the best of my knowledge, the official Delta Airlines app installed from the Play Store.
A Twitter search suggests that a lot of people got the same message. It appears to be an error at Delta. What I don't know is whether there's any way to confirm that a particular message came from the app vs spoofed it in some way.