how to get python unit test overwrite variable from imported package

Question

Trying to figure out how to overwrite a variable during unit testing:

#mainscript.py
import json

org_file = 'unitfile.json'

def load_json (file_name):
    with open ('{0}'.format(org_file)) as f:
       json_object =  json.load(f)
    return json_object

new_file = load_json(org_file)

def print_me():
    return (new_file['text'])

def main():
    print_me()

if __name__ == '__main__':
    main()

Unit test:

#test_mainscript.py
import json
import mainscript
import unittest
from  unittest.mock import patch

class Testmainscript(unittest.TestCase):
    # def setUp(self):
        # Not needed when using mock
    @patch('mainscript.org_file','unitfile2.json')
    def test_print_me(self):
        self.assertEqual(mainscript.org_file, 'unitfile2.json') # Correctly overwrites file
        self.assertEqual(mainscript.print_me(),'Bye World') #does not pass, still reading unitfile.json instead of unitfile2.json
if __name__ == '__main__':
    unittest.main()

This test should fail because because I'm overwriting org_file with unitestfile2.json (which contains {'text':'Bye World'}) instead of unittestfile.json (which contains {'text':'Hello World'})

But its currently passing because the variable isn't being overwritten

ahmed · Accepted Answer · 2022-05-02 20:27:51Z

1

What you are looking for is called "mocking", an example for your case:

import json
import mainscript
import unittest
from unittest.mock import patch

class Testmainscript(unittest.TestCase):
    # def setUp(self):
        # Not needed when using mock
 
    @patch('mainscript.org_file', 'unitfile2.json')
    def test_print_me(self):
        self.assertEqual(mainscript.print_me(),'Hello World')

if __name__ == '__main__':
    unittest.main()

edited May 2, 2022 at 20:27

answered Apr 30, 2022 at 2:02

ahmed

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8 Comments

chowpay Over a year ago

I'm still getting a passing result are you sure its mocking unitfile with unitfile2?

ahmed Over a year ago

Not sure, It's how this is done but might need some changes, You can add a test to see if it does change: self.assertEqual(mainscript.org_file, 'unitfile2.json')

chowpay Over a year ago

I added the test AssertionError: <Mock id='140009482389680'> != 'unitfile2.json' . Im pretty sure its not mocking correctly

ahmed Over a year ago

Try this: @patch('mainscript.org_file', 'unitfile2.json')

ahmed Over a year ago

I see, you need to make with open(... a function and call it in print_me to get the content, because your code now load the text before it get patched

|

chowpay · Accepted Answer · 2022-05-02 18:11:42Z

I found the issue is that I am overwriting the file as expected but when I call the test I am not using the mocked file. Wrapping the function seemed to work:

#mainscript.py
import json


org_file = 'unitfile.json'
def load_json (json_file):
    with open ('{0}'.format(org_file)) as f:
       json_object =  json.load(f)
    return json_object


def print_me(df_file):
    return (df_file['text'])

def main():
    print_me()

if __name__ == '__main__':
    main()

Here I used the wrapped patch as an input

#test_mainscript.py
import json
import mainscript
import unittest
from  unittest.mock import patch

class Testmainscript(unittest.TestCase):
    @patch('mainscript.org_file','unitfile2.json')
    def test_print_me(self):
        self.assertEqual(mainscript.org_file, 'unitfile2.json')
        self.assertEqual(mainscript.print_me(mainscript.load_json(mainscript.org_file)),'Bye World')

if __name__ == '__main__':
    unittest.main()

Test now work:

----------------------------------------------------------------------
Ran 1 test in 0.000s

OK

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