code: def test_structure_tensor_3d_rc_only():
      cube = np.zeros((5, 5, 5))
      with pytest.raises(ValueError):
          structure_tensor(cube, sigma=0.1, order="xy")
      A_elems_rc = structure_tensor(cube, sigma=0.1, order="rc")
      A_elems_none = structure_tensor(cube, sigma=0.1)
      assert_array_equal(A_elems_rc, A_elems_none)
  
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 4 for calling a global function with example usage: test_structure_tensor_3d_rc_only() without return types