code: def test_write_bigheader_file(self):
      tractogram = Tractogram(
          DATA["streamlines"], affine_to_rasmm=np.eye(4)
      )
  
      # Offset is represented by 2 characters.
      tck_file = BytesIO()
      tck = TckFile(tractogram)
      tck.header["new_entry"] = " " * 20
      tck.save(tck_file)
      tck_file.seek(0, os.SEEK_SET)
  
      new_tck = TckFile.load(tck_file)
      assert_tractogram_equal(new_tck.tractogram, tractogram)
      assert new_tck.header["_offset_data"] == 99
  
      # We made the jump, now offset is represented by 3 characters
      # and we need to adjust the offset!
      tck_file = BytesIO()
      tck = TckFile(tractogram)
      tck.header["new_entry"] = " " * 21
      tck.save(tck_file)
      tck_file.seek(0, os.SEEK_SET)
  
      new_tck = TckFile.load(tck_file)
      assert_tractogram_equal(new_tck.tractogram, tractogram)
      assert new_tck.header["_offset_data"] == 101
  
imports: import os
  import unittest
  from io import BytesIO
  from os.path import join
  import numpy
  import pytest
  from numpy.testing import assert_array_equal
  from ...testing import data_path, error_warnings
  from ..None import tck
  from ..array_sequence import ArraySequence
  from ..tck import TckFile
  from ..tractogram import Tractogram
  from ..tractogram_file import DataError, HeaderError, HeaderWarning
  from .test_tractogram import assert_tractogram_equal
label_desc: Use image node_id 13 for calling the TestTCK obj's underlying member method code with example usage: obj.test_write_bigheader_file() without return types