import unittest
from unittest.mock import patch, Mock


class UnderTest():

    def __init__(self, param):

        if isinstance(param, int):
            raise ProductionError(f'param {param} should be an integer', 'message2')


class ProductionError (Exception):

    def __init__(message1, message2):

        # do something in production code
        pass


class MockError (ProductionError):

    def __init__(*args):
        # it seems as no argument is passed here

        print(args[1], args[0])


class Test (unittest.TestCase):
    def setUp(self):
        patcher = patch('__main__.ProductionError', instance=True, side_effect=MockError)
        self.mockerror = patcher.start()
        self.addCleanup(patcher.stop)

    def test_undertest(self):

        object = UnderTest(1)


if __name__ == '__main__':
    unittest.main()