> Cleanup on test failure is supposed to be done.  Cleanup on crash or 
> buildbot timeout isn't done as far as I know (and that was a concern I
> had with the changes made to support.TESTFN and the cwd, but I didn't
> articulate it very well).  

Ah, yeah, this is almost certainly to do with crash/timeout.  I remember running into this way back in 2008 when I was running a few slaves.

Personally I think the best solution is to have the test framework allocate a single test directory, inform the parent* as to what it is, then make sure all temp files are rooted in it.  The parent* should then rm -rf the tempdir at the end of the run as a final 'catch all'.

parent*: this will mean different things in different contexts... could be the Tools/run_tests.py wrapper, buildbot slave wrapper, etc.