Assert a function is not executed in Python unittest

What I would do is to use mock. Mock the function and assert that mock_function.call_count==0.

You can read more about mock here:
https://docs.python.org/3/library/unittest.mock.html

I'd like to answer my own question. So far my solution is using Mock.call. Example this is where reset password function located: utils/password.py

class Password(object):

    def reset(self):
        ...

So I need to mock this object at my test code test/login.py

@patch('utils.password.Password.reset')
def test_wrong_password(self, mocked_password_reset):
    ...
    assert mocked_password_reset.called == False

use mock.patch.object and assert_not_called or call_count to do this. assume you function define in mymodule.py:

def function_can_not_be_called():
    pass

def func(call):
    if call:
        function_can_not_be_called()

test code in test_mymodule.py

import mymodule
import unittest
from mock import patch

class CTest(unittest.TestCase):

    @patch.object(mymodule, "function_can_not_be_called")
    def test_MockFunc(self, mock_func):
        mymodule.func(0)
        mock_func.assert_not_called()

        mymodule.func(1)
        mock_func.assert_called_once()

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