My workstation was failing a test because it didn't have a 640x480 display mode. Turned out it was how the dual monitor support was configured, and changing a line in /etc/X11/xorg.conf from Option "MetaModes" "2560x1600,2560x1600; 1920x1200,1920x1200; 1600x1200,1600x1200; 1280x1024,1280x1024" to Option "MetaModes" "2560x1600,2560x1600; 1920x1200,1920x1200; 1600x1200,1600x1200; 1280x1024,1280x1024; 640x480,NULL" made the test happy.
Probably not worth worrying about changing the test to expect crazy configurations like this...