code: def test_spikes_alpha_op(self):
      spikes = Spikes(
          [(0, 0, 0), (0, 1, 0.2), (0, 2, 0.7)], vdims=["y", "alpha"]
      ).opts(alpha="alpha")
      msg = 'ValueError: Mapping a dimension to the "alpha" style'
      with pytest.raises(AbbreviatedException, match=msg):
          mpl_renderer.get_plot(spikes)
  
imports: import numpy
  import pytest
  from holoviews.core.options import AbbreviatedException
  from holoviews.core.overlay import NdOverlay
  from holoviews.core.spaces import HoloMap
  from holoviews.element import Spikes
  from ..utils import ParamLogStream
  from .test_plot import TestMPLPlot, mpl_renderer
label_desc: Use image node_id 16 for calling the TestSpikesPlot obj's underlying member method code with example usage: obj.test_spikes_alpha_op() without return types