In some terminals emulators, running

     env -u DISPLAY aatest

and pressing Enter three times makes aa-test spew "error!" messages
continuously.

I've reproduced this with:

• Linux console (TERM=linux)
• urxvt (TERM=rxvt-unicode-256color)
• stterm (TERM=st-256color)
• mlterm (TERM=mlterm)
• alacritty (TERM=alacritty)

So I guess it's everything that's not (pretending to be) xterm?