How to mock Python static methods and class methods

Question

How do I mock a class that has unbound methods? For example, this class has a @classmethod and a @staticmethod:

class Calculator(objec         


        

Answer 1

One way to do it is

def test_increment(mocker):
    mocker.patch.object(Calculator, attribute='increment', return_value=10)
    ...actual test code...

Answer 2

You were patching the wrong object. You must patch the Calculator from the Machine class, not the general Calculator class. Read about it here.

from mock import patch
import unittest

from calculator import Calculator
from machine import Machine


class TestMachine(unittest.TestCase):
    def my_mocked_mult(self, multiplier):
        return 2 * multiplier * 3
    def test_bound(self):
        '''The bound methods of Calculator are replaced with MockCalculator'''
        machine = Machine(Calculator(3))
        with patch.object(machine, "mult") as mocked_mult:
            mocked_mult.side_effect = self.my_mocked_mult
            self.assertEqual(machine.mult(3), 18)
            self.assertEqual(machine.incr_bound(3), 5)
            self.assertEqual(machine.decr_bound(3), 1)

    def test_unbound(self):
        '''Machine.incr_unbound() and Machine.decr_unbound() are still using
        Calculator.increment() and Calculator.decrement(n), which is wrong.
        '''
        machine = Machine(Calculator(3))
        self.assertEqual(machine.incr_unbound(3), 4)    # I wish this was 5
        self.assertEqual(machine.decr_unbound(3), 2)    # I wish this was 1