Run the xbench test suite quickly as a first pass integrity check:
$ xbench -timegoal 1 -nruns 1This should take only a few minutes and the X server should not crash. If you watch the screen, the patterns should appear normally and no unusual drawing activity should take place.
If that quick run works properly, run xbench without arguments for a 30 minute stress test of the xserver:
$ xbenchThe X server should not crash and the test should complete.
See xbench and RunTests.