code: def test_label_alpha_op_update(self):
      labels = HoloMap(
          {
              0: Labels(
                  [(0, 0, 0.3), (0, 1, 1), (0, 2, 0.6)], vdims="alpha"
              ),
              1: Labels(
                  [(0, 0, 0.6), (0, 1, 0.1), (0, 2, 1)], vdims="alpha"
              ),
          }
      ).opts(alpha="alpha")
      plot = mpl_renderer.get_plot(labels)
      artist = plot.handles["artist"]
      self.assertEqual([a.get_alpha() for a in artist], [0.3, 1, 0.6])
      plot.update((1,))
      artist = plot.handles["artist"]
      self.assertEqual([a.get_alpha() for a in artist], [0.6, 0.1, 1])
  
imports: import numpy
  from holoviews.core.dimension import Dimension
  from holoviews.core.options import Cycle
  from holoviews.core.spaces import HoloMap
  from holoviews.element import Labels
  from holoviews.plotting.util import rgb2hex
  from .test_plot import TestMPLPlot, mpl_renderer
label_desc: Use image node_id 13 for calling the TestLabelsPlot obj's underlying member method code with example usage: obj.test_label_alpha_op_update() without return types