How to mock a variable from another module in python3? - python-unittest

Question

Below is my source code
#src.py
from common.configs import MANDATORY_FIELDS
def check_mf():
if set(MANDATORY_FIELDS).issubset(['a','b','c']):
return True
else:
raise Exception("Error in mandatory fields")
And here is my test code
#test_src.py
from unittest import TestCase, main, mock
from src import check_mf
class TestMailSenderUtil(TestCase):
def test_method(self):
with mock.patch('src.MANDATORY_FIELDS') as mocked_mf:
mocked_mf.return_value = ['a','b','c','d']
self.assertRaises(ValidationException, check_mf)
when i run this code the test is not passing. It throws an error saying that
AssertionError: ValidationException not raised by check_mf
Why do i get this error?
FYI, when i try to print MANDATORY_FIELDS in src.py file while running unittesting i get this
<MagicMock name='MANDATORY_FIELDS' id='139766761401144'>
Why the mocking is not working here?

Answer 1

There is no return_value for a variable MANDATORY_FIELDS. Just pass new value as second parameter for patch().
E.g. (Python 3.9.2)
src.py:
from configs import MANDATORY_FIELDS
class ValidationException(Exception):
pass
def check_mf():
print(MANDATORY_FIELDS)
if set(MANDATORY_FIELDS).issubset(['a', 'b', 'c']):
return True
else:
raise ValidationException("Error in mandatory fields")
configs.py:
MANDATORY_FIELDS=['a']
test_src.py:
from unittest import TestCase, main, mock
from src import check_mf, ValidationException
class TestMailSenderUtil(TestCase):
def test_method(self):
with mock.patch('src.MANDATORY_FIELDS', ['a', 'b', 'c', 'd']) as mocked_mf:
self.assertRaises(ValidationException, check_mf)
if __name__ == '__main__':
main()
unit test result:
['a', 'b', 'c', 'd']
.
----------------------------------------------------------------------
Ran 1 test in 0.000s
OK
Name Stmts Miss Cover Missing
----------------------------------------------------------------------
src/stackoverflow/68162471/configs.py 1 0 100%
src/stackoverflow/68162471/src.py 8 1 88% 9
src/stackoverflow/68162471/test_src.py 8 0 100%
----------------------------------------------------------------------
TOTAL 17 1 94%