При проверке py.test --pep8 ругается на exit(10) — что не так?

if (len(sys.argv) != 2):
    print('Usage: {} object_id'.format(sys.argv[0]))
    exit(10)

sasha@admin ~/Py-dev/docx $ py.test --pep8 merge.py 
================================== test session starts ==================================
platform linux -- Python 3.5.2, pytest-3.8.0, py-1.6.0, pluggy-0.7.1
rootdir: /home/sasha/Py-dev/docx, inifile:
plugins: pep8-1.0.6
collected 1 item / 1 errors                                                             

======================================== ERRORS =========================================
_______________________________ ERROR collecting merge.py _______________________________
merge.py:27: in <module>
    exit(10)
/usr/lib/python3.5/_sitebuiltins.py:26: in __call__
    raise SystemExit(code)
E   SystemExit: 10
------------------------------------ Captured stdout ------------------------------------
Usage: /usr/local/bin/py.test object_id
!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!!!!!!!!
================================ 1 error in 0.20 seconds ================================