How can I test a display resolution that's not listed?
To see all graphics supported modes use the alt key before clicking on Scaled in display preferences.

To see it in 19:9 use a Thunderbolt cable to a TV. (assuming you have those)

If you have a Mac like I do (MBA 2012) then using the Thunderbolt you can get up to 2560 by 1600 pixels on your HDTV.

Intel HD Graphics 4000
Dual display and video mirroring:
Simultaneously supports full native resolution on the built-in display and up to 2560 by 1600 pixels on an external display, both at millions of colors