Mock a function present inside a list in pytest

Question

I want to mock a function present inside a list and check whether it has been called at least once. Below is a similar implementation I tried:-

In fun_list.py (funA and funB are two functions in other_module)

import other_module

FUN_LIST = [
    other_module.funA,
    other_module.funB,
]

def run_funs():
    for fun in FUN_LIST:
        fun()

In demo.py

from fun_list import run_funs

def run_demo():
    ...
    run_funs()
    ...

In test_demo.py

from demo import run_demo

@patch('other_module.funB')
def test_demo_funs(mocked_funB):
    mocked_funB.return_value = {}
    run_demo()

    assert mocked_funB.called

In above case, I'm trying to mock funB in other_module but the function doesn't get mocked and the cursor gets inside the actual funB in other_module. Thus, the assert mocked_funB.called returns false.

Any lead on how I can mock other_module.funB ? I have found a similar question on StackOverflow but that went unanswered, so decided to post my version of it.

Any help will be appreciated, thank you in advance.

score 1 · Accepted Answer · answered May 17 '21 at 05:01

You need to mock before importing the module under test. The code in the module scope will be executed when import the module. It is too late to mock through the decorator when the test case is executed.

E.g.

other_module.py:

def funA():
    pass


def funB():
    pass

fun_list.py:

import other_module

print('execute module scope code')

FUN_LIST = [
    other_module.funA,
    other_module.funB,
]


def run_funs():
    for fun in FUN_LIST:
        fun()

demo.py:

from fun_list import run_funs


def run_demo():
    run_funs()

test_demo.py:

import unittest
from unittest.mock import patch


class TestDemo(unittest.TestCase):
    @patch('other_module.funB')
    def test_demo_funs(self, mocked_funB):
        print('mock before import the module')
        from demo import run_demo
        mocked_funB.return_value = {}
        run_demo()
        assert mocked_funB.called


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

test result:

mock before import the module
execute module scope code
.
----------------------------------------------------------------------
Ran 1 test in 0.002s

OK
Name                                         Stmts   Miss  Cover   Missing
--------------------------------------------------------------------------
src/stackoverflow/67563601/demo.py               3      0   100%
src/stackoverflow/67563601/fun_list.py           6      0   100%
src/stackoverflow/67563601/other_module.py       4      1    75%   6
src/stackoverflow/67563601/test_demo.py         12      0   100%
--------------------------------------------------------------------------
TOTAL                                           25      1    96%

Hi @slideshowp2, thanks a ton. That surely clears out my confusion regarding it. I will accept this answer. Just one last query, I'm having multiple such test functions that is mocking funB and calling run_demo(). If an earlier function calls it successfully, the other subsequent patches are failing (perhaps because of the same reason you mentioned). Any solution to that front ? — Mr_Somebody, May 17 '21 at 09:31
The call to run_demo() in my case is actually a client.post() call made using @pytest.mark.django_db decorator. — Mr_Somebody, May 17 '21 at 09:33
@Mr_Somebody You'd better ask a new question with minimal, reproducble example — Lin Du, May 17 '21 at 09:34

Mr_Somebody · Answer 2 · 2021-05-19T01:33:11.207

I took the lead from @slideshowp2's answer and have modified things a bit differently. In my case I was having multiple such test functions that is mocking funB and calling run_demo (originally a client.post() call from Django.test). If an earlier function calls it successfully, the other subsequent patches were failing (because of the same reason stated by @slideshowp2). So, I changed the approach to this :-

In fun_list.py (funA and funB are two functions in other_module)

import other_module

FUN_LIST = [
    'funA',
    'funB',
]

def run_funs():
    for fun in FUN_LIST:
        getattr(other_module, fun)()

In demo.py

from fun_list import run_funs

def run_demo():
    ...
    run_funs()
    ...

In test_demo.py

from demo import run_demo

@patch('other_module.funB')
def test_demo_funs(mocked_funB):
    mocked_funB.return_value = {}
    run_demo()

    assert mocked_funB.called

Mock a function present inside a list in pytest

2 Answers2