from unittest.mock import patch
from unittest import TestCase, main


class MockedClass:

    def real_method(self):
        print('___')
        print('Реальный метод')
        print('Выполняется реальная работа')
        print('___')

        return 'OK'


class MyTestCase(TestCase):

    def test_real_method(self):
        mocked_class = MockedClass()
        result = mocked_class.real_method()
        self.assertEqual(result, 'OK')

    @patch('__main__.MockedClass.real_method')
    def test_real_method_mocked(self, mock_real_method):
        mock_real_method.return_value = 'NOT OK'
        mocked_class = MockedClass()
        result = mocked_class.real_method()
        self.assertEqual(result, 'NOT OK')


main()