How can I perform automated testing for popup validation?

[longbuibao]

In my application, I have some validation logic. I also want to write an end-to-end test to ensure that the app displays an error when the input value is invalid.

Currently, I've noticed that the popup does not have accessibility information:

How can I automate validation testing in this case? Something like:
GetErrorPopup().GetText() == "Expected error message"