As far as I know, Mega CD doesn't have copy protection so homebrew apps like the 240p test suite should work fine off CD-R. Mega CD is region locked though, so I would think you would need NTSC-Japan header info for it to work on your JP Mega CD.
Thanks guys.Homebrew software for Sega consoles should be region-free, because it's really easy and straightforward to add the required information to the game header.
Just try it out.
Downloaded the suite following the link in the OP, and I found out there are all the three ISOs - American, European and Japanese - into the zip file, so I'll just burn the JP one and give it a try.