stubs.py

import unittest
from unittest import mock


class SomeClass:
    def a_method(self):
        return 2


class TestStub(unittest.TestCase):
    def setUp(self):
        self.patchers = []

    def stub(self, obj, method_name, func):
        patcher = mock.patch.object(obj, method_name, func)
        patcher.start()
        self.patchers.append(patcher)

    def test_patching(self):
        self.stub(SomeClass, 'a_method', lambda self: 3)

        s = SomeClass()

        assert s.a_method() == 3

    def tearDown(self):
        for patcher in self.patchers:
            patcher.stop()