Tests for the posix module should go in test_posix. The name 'posix' is used very loosely in python, it is basicly used as an alias for 'unixy'.

I'm not too happy about replicating the definition of the flags, as Ned noted the flags are also defined in Lib/stat.py.  I'd keep them out of posixmodule as the current definitions in Lib/stat.py should be valid on all platforms that currently support these flags.

W.r.t testing: there should be some simple smoke tests, basicly just enough to ensure that the function is available and that it links up to the right system call. There is no need to perform un exhaustive test of the system call, that should be done by the os vendor.