Python mocking the right class/import

I am trying to implement unittests for my python program. The problem is, that my program is using several imported classes, which I would like to replace by a mocked object/class to verify single functions/methods.

I do not get any errors with my mocked class. But it appears that the mock itself didn't replace the object I wanted to replace.

This is basically my structure:

First the class I want to mock. Might look like that:

class ToMock():
    def getSomething(self):
        return "something"

The class I want to test looks like this:

from x.y import ToMock

class ClassToTest():
    def __init__(self):
        self.obj = ToMock()

    def returnStuff():
        return self.obj.getSomething()

As you can imagine, I want to test the returnStuff method. Therfore I want to mock .getSomething, or better said the whole ToMock object.

The unittest should therefore test the ClassToTest with the mocked ToMock class. I tried several mock.patch variants, but I couldn't get it to run/test properly.

import unittest
from unittest import mock

from a.b import ClassToTest

class TestObject(unittest.TestCase):
    def setUp(self):
        with mock.patch('x.y.ToMock') as mock_obj:
            mock_obj.return_value.getSomething().return_value="mocked return value"
            self.test_class = ClassToTest()
            result = self.test_class.returnStuff() # This should return now 'mocked return value', I guess?
            mock_obj.return_value.getSomething.assert_called_once_with("")

The problem I face is, that the self.test_class.returnStuff() is not "calling" the mocked object, but imports the real class etc. and therefore I am running into timeouts, or similar stuff.

I am sure, that I provide the wrong path for the object which should be mocked. Perhaps someone can hint me into the right direction.

Thanks -GreNait

Copyright Notice：Content Author:「GreNait」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/66548920/python-mocking-the-right-class-import