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_y_datetime(self):
      x = [14, 15, 16]
      y = np.array(["2023-09-01", "2023-09-03"], dtype="datetime64")
      z = np.array([[0, 1, 0], [0, 1, 0]])
      img = Image((x, y, z))
      op_contours = contours(img, levels=[0.5])
      # Note multiple lines which are nan-separated.
      np.testing.assert_array_almost_equal(
          op_contours.dimension_values("x").astype(float),
          [14.5, 14.5, np.nan, 15.5, 15.5],
      )
  
      tz = dt.timezone.utc
      expected_y = np.array(
          [
              dt.datetime(2023, 9, 3, tzinfo=tz),
              dt.datetime(2023, 9, 1, tzinfo=tz),
              np.nan,
              dt.datetime(2023, 9, 1, tzinfo=tz),
              dt.datetime(2023, 9, 3, tzinfo=tz),
          ],
          dtype=object,
      )
  
      # Separately compare nans and datetimes
      y = op_contours.dimension_values("y")
      mask = np.array(
          [True, True, False, True, True]
      )  # Mask ignoring nans
      np.testing.assert_array_equal(y[mask], expected_y[mask])
      np.testing.assert_array_equal(
          y[~mask].astype(float), expected_y[~mask].astype(float)
      )
  
      np.testing.assert_array_almost_equal(
          op_contours.dimension_values("z"), [0.5] * 5
      )
  
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 13 for calling the OperationTests obj's underlying member method code with example usage: obj.test_image_contours_y_datetime() without return types