Mocking private methods in python

gistfile1.py

""" This is a simple gist to show how to mock
private methods. I've got lots of questions
regarding this topic. Most people seems confused.

Hope it helps.
"""


import unittest
import mock


class Car:
    def __private(self):
        return 1

    def no_private(self):
        return self.__private()


class CarTest(unittest.TestCase):

    def test_exception_raises(self):
        c = Car()
        with self.assertRaises(AttributeError):
            c.__private()

    def test_car_works(self):
        c = Car()
        self.assertEqual(c.no_private(), 1)

    def test_mock_private(self):
        c = Car()
        with mock.patch.object(c, '_Car__private', return_value=3) as method:
            c.no_private()
            method.assert_called_once_with()

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

+1

ty!

wow very simple and clear

Excelsior!!

this works for me as well (and is nicer when you have to patch more than one private method):

@mock.patch.object(Car, "_Car__private")
def test_mock_private(self, method):
    c = Car()
    c.no_private()
    method.assert_called_once_with() 

this works for me as well (and is nicer when you have to patch more than one private method):

@mock.patch.object(Car, "_Car__private")
def test_mock_private(self, method):
    c = Car()
    c.no_private()
    method.assert_called_once_with() 

🥇

great stuff 😄 thank you

There is a way to mock private class attribute?
For example in the following code it's possibile patch __private_attribute to set it to 2?

class Car:    
	__init__(self):
		self.__private_attribute = 1

	def use_private_attribute:
		If self.__private_attribute > 2:
			return True
		else:
			return False

	def __private(self):      
		  return 1

   	def no_private(self):       
		return self.__private()

@damorosodaragona that's an instance method, and it should work in the same way.

@santiagobasulto if i try to patch self.__private_attribute in the same way that you shown i got "no attribute error" from mock

@damorosodaragona use this:

from mock import patch, PropertyMock
with mock.patch.object(c, '_Car __private_attribute', new_callable=PropertyMock) as mock:
    mock.return_value = 4. # the value of the attr