An extremely preliminary (v0.1) version of the 240p Test Suite has recently been ported over to the Saturn by a user over on SegaXtreme who goes by hitomi2500.
Link to download
Article about it from RetroRGB
It's a little rough around the edges, but it seems to work fine on the latest stable and unstable Saturn cores for MiSTer, assuming you set your region to USA.
The only thing weird about it is that the core doesn't seem to pass the drop shadow test in 240p. It works as expected in the other video modes. I'm not sure if this is a problem with the core in its current state, or with the implementation of the 240p test suite, considering it's a first release alpha version. I kinda want to test it on real hardware, but my Saturn's in storage and it would be a bit difficult to dig it up and test it out right now