python unit test with mock for checking file path

Question

I have following python function in 'au.py' :

import os

def resolv_conf_audit():
    ALT_PATH = "/etc/monitor/etc/resolv.conf.{}".format(os.uname()[1])
    RES_PATH = "/data/bin/resolvconf"
    if os.path.isfile(RES_PATH):

        return "PASSED", "/data/bin/resolvconf is present"

    elif os.path.isfile(ALT_PATH):
        return "PASSED", "/etc/monitor/etc/resolv.conf. is present"

    else:
        return "FAILED"

I need to write a unit test with mock which can check the path exists or not following is the unit test which I wrote

from au import resolv_conf_audit
import unittest
from unittest.mock import patch


class TestResolvConf(unittest.TestCase):
    @patch('os.path.isfile.ALT_PATH')
    def test_both_source_files_not(self, mock_os_is_file):
        mock_os_is_file.return_value =  False
        assert resolv_conf_audit() == "FAILED"

but I am getting following error

AttributeError: <function isfile at 0x10bdea6a8> does not have the attribute 'ALT_PATH'

How do I mock to check the presence of ALT_PATH and RES_PATH so that I can validate the function. In future this unit test should have the capability to mock removal some files, before writing that I am testing this simple one

Mauro Baraldi · Accepted Answer · 2020-05-28 20:35:33Z

1

Mocks by definition is a way to simulate beahvior of objects. You are trying to handle a variable (ALT_PATH) inside your function.

All you need is to mock just the os.path.isfile method.

class TestResolvConf(unittest.TestCase):

    @patch('os.path.isfile')
    def test_both_source_files_not(self, mock_os_is_file):
        mock_os_is_file.return_value =  False
        assert resolv_conf_audit() == "FAILED"

    @patch('os.path.isfile')
    def test_both_source_files_exists(self, mock_os_is_file):
        mock_os_is_file.return_value =  True
        assert resolv_conf_audit() == "PASSED"

edited May 28, 2020 at 20:35

answered May 28, 2020 at 18:04

Mauro Baraldi

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2 Comments

lincolnadym Over a year ago

Newbie question, Where does mock_os_is_file come from or gets created? Is it a default thing created by @patch('os.path.isfile')?

Mauro Baraldi Over a year ago

This is the name you can give to mock object. I could be banana, but it may not make sense for the context :-P

Rajesh P S · Accepted Answer · 2020-05-29 02:14:04Z

1

Thanks @ Mauro Baraldi, as per your suggestion, I changed the code little bit and it works fine now

    def test_both_source_files_not(self, mock_os_is_file):
        mock_os_is_file.side_effect = [False , False]
        assert resolv_conf_audit() == "FAILED"

answered May 29, 2020 at 2:14

Rajesh P S

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