PYTHON setup.py build_ext --inplace
PYTHON test_error_pos.py

######## setup.py ###########
from distutils.core import setup
from Cython.Build import cythonize

setup(ext_modules=cythonize("error_pos.pyx"))

######## error_pos.pyx ###########
from os import *

abcdefg(line)

######## test_error_pos.py ###########
import subprocess
import sys

cmd = [sys.executable, '-c', 'import error_pos']
proc = subprocess.Popen(cmd, stderr=subprocess.PIPE)
_, err = proc.communicate()
# The error should contain the line number and the line text where the
# undefined identifier is used.
assert b'line 3, in init error_pos' and b'abcdefg(line)' in err, err