The unit test for our simple exception_example, uses side_effect to trigger the exception.

exception_example_test.py

import exception_example
import unittest
import mock


class ExceptionExampleTest(unittest.TestCase):
    def test_does_user_exist(self):
        self.assertTrue(exception_example.does_user_exist("user1"))

    def test_does_user_exist_no_user(self):
        with mock.patch("exception_example.find_user", autospec=True, side_effect=Exception):
            self.assertFalse(exception_example.does_user_exist("user2"))


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