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) == self._pixdim_message
  
imports: import io
  from os.path import dirname
  from os.path import join
  import numpy
  import pytest
  from numpy.testing import assert_array_almost_equal
  from packaging.version import Version
  import nibabel
  from nibabel import cifti2
  from nibabel.cifti2.parse_cifti2 import _Cifti2AsNiftiHeader
  from nibabel.tests import test_nifti2
  from nibabel.tests.nibabel_data import get_nibabel_data, needs_nibabel_data
  from nibabel.tmpdirs import InTemporaryDirectory
label_desc: Use image node_id 1 for calling the TestCifti2SingleHeader obj's underlying member method code with example usage: obj.test_pixdim_checks() without return types