I have some comments about this omission  (from line 70 to 79)

The outer try-finally clause will not swallow exceptions as I understand, the try clause
is executed, which may raise exceptions but the raising of these exceptions will be delayed
to after executing the finally clause. I made this to ensure cleaning up temp files
that are generated by the test no matter what the test result was. There is no except
clause in this outer statement so exceptions are not suppressed

The purpose of the inner try-except clause is to suppress errors resulting from 
multiple processes trying to delete the same directory. The process that reach this
code first will delete the directory. Other processes will raise an exception because
the directory no longer exist.

I think now at the current setting the test will never pass in parallel? at least this is what I am seeing.