class_docstr: Tests allowable data formats when constructing
  the basic Element types.
class_docstr_tok: ["Tests","allowable","data","formats","when","constructing","the","basic","Element","types","."]
code: def test_image_contours_filled_auto_levels(self):
      z = np.array([[0, 1, 0], [3, 4, 5], [6, 7, 8]])
      img = Image(z)
      for nlevels in range(3, 20):
          op_contours = contours(img, filled=True, levels=nlevels)
          levels = [item["z"] for item in op_contours.data]
          assert len(levels) <= nlevels + 1
          delta = 0.5 * (levels[1] - levels[0])
          assert np.min(levels) <= z.min() + delta
          assert np.max(levels) >= z.max() - delta
  
imports: import datetime
  from unittest import skipIf
  import numpy
  import pandas
  import pytest
  from holoviews import Area, Contours, Curve, Dataset, GridSpace, Histogram, HoloMap, Image, NdLayout, NdOverlay, Points, Polygons, QuadMesh, renderer
  from holoviews.core.data.grid import GridInterface
  from holoviews.element.comparison import ComparisonTestCase
  from holoviews.operation.element import contours, decimate, gradient, histogram, interpolate_curve, operation, threshold, transform
label_desc: Use image node_id 23 for calling the OperationTests obj's underlying member method code with example usage: obj.test_image_contours_filled_auto_levels() without return types