Simple example of mocking two functions for the purpose of testing.

users_test.py

import unittest
import mock
import users
import file_utils


class UsersTest(unittest.TestCase):
    _file_path = "SOME FILE PATH"

    def test_get_users(self):
        user = "user1"

        # create a mock for read_file which returns the value user
        file_utils.read_file = mock.MagicMock(name="read_file", return_value=user)

        result = users.get_users()

        self.assertEqual(user, result)
        file_utils.read_file.assert_called_once_with(self._file_path)

    def test_save_users(self):
        # create a simple mock for write file
        file_utils.write_file = mock.MagicMock(name="write_file")

        test_users = "user1"
        users.save_users(test_users)
        file_utils.write_file.assert_called_with(self._file_path, test_users)

        test_users = "user1, user2"
        users.save_users(test_users)
        file_utils.write_file.assert_called_with(self._file_path, test_users)


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