> > You have eaten "return NULL;" in posix_mkfifo.
> What do you mean?

You deleted "return NULL;" after "if (!PyArg_ParseTuple(...))" in the 
posix_mkfifo() function.

> > Tests should check that results for unicode filename is same as for str
> > filename.
> What do you mean? Can you provide an example?

For example test_statvfs should check that os.statvfs(TESTFN_UNICODE) == 
os.statvfs(TESTFN_UNICODE_ENCODED) (where TESTFN_UNICODE_ENCODED is relevant 
8-bit str).