Most importantly, the scope needs to be perfectly cooled before considering a star test.
The first link shows a decent sct, with no greatly brighter/dimmer inner or outer rings and just a moderate difference in the size of the central shadow on either side of focus:
http://aberrator.astronomy.net/scope...rain250_1.html
The second link shows a poorer quality sct with obvious differences in brightness across the rings, a bright inner ring on one side of focus and a bright outer ring on the other side, and a bit larger difference in the size of the central shadow on either side of focus:
http://aberrator.astronomy.net/scope...ain_200_4.html
I don't know that much about star testing and it's easy to misinterpret the star test. I can say from experience that a crappy sct will still show more detail than a good refractor half its aperture simply by virtue of the greater resolving ability of the bigger aperture - it's easy to get overly worried about optical quality(worth worrying about in the warranty period though).
'Star Testing Astronomical Telescopes' by Suiter is a good book if you want to learn more. Hope that helps.