Code for http://stackoverflow.com/q/18573542/599884

my_script.py

#!/usr/bin/python
import sys

with open(sys.argv[1],'r') as input_file:
    print input_file.read()

tests-arg_file.txt

--Contents of arg_file.txt--

tests-conftest.py

# content of tests/conftest.py
import pytest
import os, shutil

BASEDIR = os.path.dirname(__file__)

@pytest.fixture()
def set_up(tmpdir):
    """Create tmpdir, copy arg_file over"""
    tmpdir.chdir()
    shutil.copyfile(os.path.join(BASEDIR, 'arg_file.txt'), 
	                os.path.join(os.getcwd(), 'arg_file.txt'))
    print('\nset_up: In directory ' + os.getcwd())

tests-test_in_scriptdir.py

# content of tests/test_in_scriptdir.py
import subprocess, shlex, os
import pytest

BASEDIR = os.path.dirname(__file__) #this points to the tests/ directory

@pytest.mark.usefixtures('set_up')
class TestInScriptdir:
    def test_1(self):
        """Execute script in script dir where my_script.py resides"""
        # remember path to tmpdir
        temporary = os.getcwd()
        # change to script directory
        os.chdir(os.path.join(BASEDIR,'..'))
        print('Running in directory ' + os.getcwd())
        # run script
        command = './my_script.py ' + os.path.join(temporary, 'arg_file.txt')
        print('Command: ' + command)
        subprocess.call(shlex.split(command),
						stderr=subprocess.STDOUT, 
						cwd=os.getcwd())

tests-test_in_tmpdir.py

# content of tests/test_in_tmpdir.py
import subprocess, shlex, os
import pytest

BASEDIR = os.path.dirname(__file__) #this points to the tests/ directory

@pytest.mark.usefixtures('set_up')
class TestInTempdir:
    def test_1(self):
        """Execute script in tmpdir where arg_file.txt resides"""
        print('Running in directory ' + os.getcwd())
        # run script
        command = os.path.abspath(os.path.join(BASEDIR, '..', 'my_script.py')) + ' arg_file.txt'
        print('Command: ' + command)
        output = subprocess.call(shlex.split(command),
								stderr=subprocess.STDOUT, 
								cwd=os.getcwd())