code: def test_default_sigma():
      a = np.zeros((3, 3))
      a[1, 1] = 1.0
      assert_array_equal(
          gaussian(a, preserve_range=True),
          gaussian(a, preserve_range=True, sigma=1),
      )
  
file_path: scikit-image/skimage/filters/tests/test_gaussian.py
imports: import numpy
  import pytest
  from numpy.testing import assert_array_equal
  from skimage._shared.utils import _supported_float_type
  from skimage.filters import difference_of_gaussians, gaussian
label_desc: Use image node_id 3 for calling a global function with example usage: test_default_sigma() without return types