How to display test image on Declink Duo 2?

We drive a Declink duo 2 in an external PCIe chassis using Thunderbolt from a mac mini. Software is ProPresenter. For the first time recently after a year of using this setup nothing was coming out of the Declink card. After a lot of futzing around, resetting, powering off/on it started working but I don't know why.

Is there an easy way to display some kind of test image, color bars, etc. on the Declink? I want to determine if ProPresenter is the problem. Video Setup doesn't seem to do it. I finally figured out how to load something into Media Express but it doesn't by default generate a static test image.

Thanks!

There is no test signal generator. I just load a clip of bars & tone into Media Express and use the "Display freeze frame when not playing" option in Desktop Video. Then you don't need to keep the clip playing.