> I ran the test with the -v option flag. The malloc error don't happen
> at the same place the hang up happens. The first one happens at:

The malloc error is normal, then, it's part of that test. It's a pity OS
X dumps something on stderr, though.

> And finally, the hang:
> 
> test_io_after_close (test.test_io.CMiscIOTest) ... ok
> test___all__ (test.test_io.PyMiscIOTest) ... ok
> test_abc_inheritance (test.test_io.PyMiscIOTest) ... ok
> test_abc_inheritance_official (test.test_io.PyMiscIOTest) ... ok
> test_abcs (test.test_io.PyMiscIOTest) ... ok
> test_attributes (test.test_io.PyMiscIOTest) ... ok
> test_blockingioerror (test.test_io.PyMiscIOTest) ... ok
> test_io_after_close (test.test_io.PyMiscIOTest) ... ok
> test_interrupted_write_buffered (test.test_io.CSignalsTest) ... <hang>

Ok. I guess you would need to investigate what happens in that
particular sub-test.