'Test get_device_info failure by failing os.listdir'

def test_get_device_info_fail(self):

    os.listdir = fail_os_listdir
    resp = self.real_app_get_device_info()
    os.listdir = self.real_listdir
    device_path = list(resp)[0]
    self.assertIsNone(resp[device_path])
