code: def test_pixdim_checks(self):
      hdr_t = self.header_class()
      for i in (1, 2, 3):
          hdr = hdr_t.copy()
          hdr["pixdim"][i] = -1
          assert self._dxer(hdr) == "pixdim[1,2,3] should be positive"
  
imports: import itertools
  import logging
  import os
  import pickle
  import re
  from io import BytesIO, StringIO
  import numpy
  import pytest
  from numpy.testing import assert_array_almost_equal, assert_array_equal
  from ..None import imageglobals
  from ..analyze import AnalyzeHeader, AnalyzeImage
  from ..arraywriters import WriterError
  from ..casting import sctypes_aliases
  from ..nifti1 import Nifti1Header
  from ..optpkg import optional_package
  from ..spatialimages import HeaderDataError, HeaderTypeError, supported_np_types
  from ..testing import assert_dt_equal, bytesio_filemap, bytesio_round_trip, data_path, suppress_warnings
  from ..tmpdirs import InTemporaryDirectory
  from .None import test_spatialimages
  from .None import test_wrapstruct
label_desc: Use image node_id 8 for calling the TestAnalyzeHeader obj's underlying member method code with example usage: obj.test_pixdim_checks() without return types