code: def test_load_unknown_format(self):
      with self.assertRaises(ValueError):
          nib.streamlines.load("")
  
imports: import os
  import tempfile
  import unittest
  import warnings
  from io import BytesIO
  from os.path import join
  import numpy
  import pytest
  from numpy.compat.py3k import asbytes
  import nibabel
  from nibabel.testing import clear_and_catch_warnings, data_path, error_warnings
  from nibabel.tmpdirs import InTemporaryDirectory
  from ..None import FORMATS, trk
  from ..tractogram import LazyTractogram, Tractogram
  from ..tractogram_file import ExtensionWarning, TractogramFile
  from .test_tractogram import assert_tractogram_equal
label_desc: Use image node_id 9 for calling the TestLoadSave obj's underlying member method code with example usage: obj.test_load_unknown_format() without return types