Mock a logger defined in the constructor using pytest - python-3.x

Question

I have this class defined:
class User():
def __init__(self):
self.logger = Logger('user.log')
def get_data(self):
_data = {
'username': 'abc'
}
_payload = json.dumps(_data)
self.logger.info("Loaded payload")
return _payload
The test case written for get_data():
#mock.patch('mymodule.file_user.Logger')
def test_get_data(self,mock_logger):
assert User().get_data() == "'username': 'abc'"
mock_logger.info.assert_called_once_with(
'Loaded payload')
The mocking here fails giving the assertion error "Expected 'info' to be called once. Called 0 times."

Answer 1

Logger is a class, self.logger.info() is an instance method. So you need to get the instance of mock_logger via .return_value.
E.g.
logger.py:
class Logger():
def __init__(self, filepath) -> None:
pass
def info(message):
print(message)
user.py:
import json
from logger import Logger
class User():
def __init__(self):
self.logger = Logger('user.log')
def get_data(self):
_data = {
'username': 'abc'
}
_payload = json.dumps(_data)
self.logger.info("Loaded payload")
return _payload
test_user.py:
import unittest
from unittest import mock
from user import User
class TestUesr(unittest.TestCase):
#mock.patch('user.Logger')
def test_get_data(self, mock_logger):
mock_logger_instance = mock_logger.return_value
user = User()
actual = user.get_data()
self.assertEqual(actual, '{"username": "abc"}')
mock_logger_instance.info.assert_called_once_with('Loaded payload')
if __name__ == '__main__':
unittest.main()
unit test result:
⚡ coverage run /Users/dulin/workspace/github.com/mrdulin/python-codelab/src/stackoverflow/66366372/test_user.py && coverage report -m --include='./src/**'
.
----------------------------------------------------------------------
Ran 1 test in 0.002s
OK
Name Stmts Miss Cover Missing
-----------------------------------------------------------------------
src/stackoverflow/66366372/logger.py 5 2 60% 3, 6
src/stackoverflow/66366372/test_user.py 13 0 100%
src/stackoverflow/66366372/user.py 10 0 100%
-----------------------------------------------------------------------
TOTAL 28 2 93%