def test_create_random_keyfile(self, mock_os_urandom):
secret = b'secret'
mock_os_urandom.return_value = secret
with patch('builtins.open', create=True) as mock_open:
mock_open.return_value = MagicMock(spec=io.IOBase)
file_handle = mock_open.return_value.__enter__.return_value
LuksDevice.create_random_keyfile('some-file')
file_handle.write.assert_called_once_with(secret)
