nsfyn55 nsfyn55 - 1 month ago 12
Python Question

Python Mocking a function from an imported module

I want to understand how to

@patch
a function from an imported module.

This is where I am so far.

app/mocking.py:

from app.my_module import get_user_name

def test_method():
return get_user_name()

if __name__ == "__main__":
print "Starting Program..."
test_method()


app/my_module/__init__.py:

def get_user_name():
return "Unmocked User"


test/mock-test.py:

import unittest
from app.mocking import test_method

def mock_get_user():
return "Mocked This Silly"

@patch('app.my_module.get_user_name')
class MockingTestTestCase(unittest.TestCase):

def test_mock_stubs(self, mock_method):
mock_method.return_value = 'Mocked This Silly')
ret = test_method()
self.assertEqual(ret, 'Mocked This Silly')

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


This does not work as I would expect. The "patched" module simply returns the unmocked value of
get_user_name
. How do I mock methods from other packages that I am importing into a namespace under test?

Answer

When you are using the patch decorator from the unittest.mock package you are not patching the namespace the module is imported from (in this case app.my_module.get_user_name) you are patching it in the namespace under test app.mocking.get_user_name.

To do the above with Mock try something like the below:

from mock import patch

class MockingTestTestCase(unittest.TestCase):

    @patch('app.mocking.get_user_name')
    def test_mock_stubs(self, test_patch):
        test_patch.return_value = 'Mocked This Silly'
        ret = test_method()
        self.assertEqual(ret, 'Mocked This Silly')

The standard library documentation includes a useful section describing this.