code: def test_update(self):
      hdr = self.header_class()
      assert hdr["num_frames"] == 0
      hdr["num_frames"] = 2
      assert hdr["num_frames"] == 2
  
imports: import os
  import warnings
  from pathlib import Path
  from unittest import TestCase
  import numpy
  import pytest
  from numpy.testing import assert_array_almost_equal, assert_array_equal
  from ..ecat import EcatHeader, EcatImage, EcatSubHeader, get_frame_order, get_series_framenumbers, read_mlist
  from ..openers import Opener
  from ..testing import data_path, suppress_warnings
  from ..tmpdirs import InTemporaryDirectory
  from .None import test_wrapstruct
  from .test_fileslice import slicer_samples
label_desc: Use image node_id 6 for calling the TestEcatHeader obj's underlying member method code with example usage: obj.test_update() without return types