code: def test_blank_image_nans():
      """Some of the corner detectors had a weakness in terms of returning
      NaN when presented with regions of constant intensity. This should
      be fixed by now. We test whether each detector returns something
      finite in the case of constant input"""
  
      detectors = [
          corner_moravec,
          corner_harris,
          corner_shi_tomasi,
          corner_kitchen_rosenfeld,
          corner_foerstner,
      ]
      constant_image = np.zeros((20, 20))
  
      for det in detectors:
          response = det(constant_image)
          assert np.all(np.isfinite(response))
  
imports: import numpy
  import pytest
  from numpy.testing import assert_almost_equal, assert_array_equal, assert_equal
  from skimage import data, draw, img_as_float
  from skimage._shared._warnings import expected_warnings
  from skimage._shared.testing import run_in_parallel
  from skimage._shared.utils import _supported_float_type
  from skimage.color import rgb2gray
  from skimage.feature import corner_fast, corner_foerstner, corner_harris, corner_kitchen_rosenfeld, corner_moravec, corner_orientations, corner_peaks, corner_shi_tomasi, corner_subpix, hessian_matrix, hessian_matrix_det, hessian_matrix_eigvals, peak_local_max, shape_index, structure_tensor, structure_tensor_eigenvalues
  from skimage.morphology import cube, octagon
label_desc: Use image node_id 30 for calling a global function with example usage: test_blank_image_nans() without return types