code: def test_sigma2fwhm():
      # Test from constant
      assert_almost_equal(sigma2fwhm(1), 2.3548200)
      assert_almost_equal(
          sigma2fwhm([1, 2, 3]), np.arange(1, 4) * 2.3548200
      )
      assert_almost_equal(fwhm2sigma(2.3548200), 1)
      assert_almost_equal(
          fwhm2sigma(np.arange(1, 4) * 2.3548200), [1, 2, 3]
      )
      # direct test fwhm2sigma and sigma2fwhm are inverses of each other
      fwhm = np.arange(1.0, 5.0, 0.1)
      sigma = np.arange(1.0, 5.0, 0.1)
      assert np.allclose(sigma2fwhm(fwhm2sigma(fwhm)), fwhm)
      assert np.allclose(fwhm2sigma(sigma2fwhm(sigma)), sigma)
  
imports: import logging
  from os.path import dirname
  from os.path import join
  import numpy
  import numpy.linalg
  from nibabel.optpkg import optional_package
  import unittest
  import pytest
  from numpy.testing import assert_almost_equal, assert_array_equal
  import nibabel
  from nibabel.affines import AffineError, apply_affine, from_matvec, to_matvec, voxel_sizes
  from nibabel.eulerangles import euler2mat
  from nibabel.nifti1 import Nifti1Image
  from nibabel.nifti2 import Nifti2Image
  from nibabel.orientations import aff2axcodes, inv_ornt_aff
  from nibabel.processing import adapt_affine, conform, fwhm2sigma, resample_from_to, resample_to_output, sigma2fwhm, smooth_image
  from nibabel.testing import assert_allclose_safely
  from nibabel.tests.test_spaces import assert_all_in, get_outspace_params
  from .test_imageclasses import MINC_3DS, MINC_4DS
label_desc: Use image node_id 1 for calling a global function with example usage: test_sigma2fwhm() without return types