Three examples of mocking, patching methods of a class.

test_patch.py

import pytest


class Simple_Class:

    def method(self):
        return 1

    def another_method(self):
        return 2


def test_instance_patch(mocker):
    simple_instance = Simple_Class()
    another_instance = Simple_Class()
    mocker.patch.object(simple_instance, "method", return_value=3)

    assert simple_instance.method() == 3
    assert another_instance.method() == 1


def test_class_patch(mocker):
    mocker.patch.object(Simple_Class, "method", return_value=3)
    simple_instance = Simple_Class()
    another_instance = Simple_Class()

    assert simple_instance.method() == 3
    assert another_instance.method() == 3


def test_class_with_side_effect(mocker):
    mocker.patch.object(Simple_Class, "method", side_effect=AttributeError("Side effect"))
    simple_instance = Simple_Class()

    with pytest.raises(AttributeError) as exception:
        simple_instance.method()
        assert exception.msg == "Side effect"