import unittest as unittest
#from six.moves import builtins
import builtins
from unittest import mock

class T1(unittest.TestCase):

    @mock.patch.object(builtins, 'open', mock.mock_open(read_data='FAKE_DATA'))
    def test_check_open(self):
        with open("some") as f:
            self.assertEqual('FAKE_DATA', f.read())


class T2(T1):pass

unittest.main()