If you're trying to see if the game will crash, try going into all of the
buildings and talking to everybody, play the first level, etc.
However, there are a lot of different components in the SNES and SWC, and
depending on which one is bad, different games may fail in different ways.
I see a lot of variation in the complaints, but the same games keep coming
up: Chrono Trigger, Seiken Densetsu 3, Final Fantasy 3, Terranigma, Donkey
Kong Country (especially the first two). All are 24/32mbit fastrom games,
which tend to stress the hardware the most, hence these are the games that
are most likely to show problems when something is flaky. But exactly what
goes wrong (glitched graphics, crashes, black screen, etc) depends on what
specifically is wrong with your hardware.