code: def test_path_continuously_varying_alpha_op(self):
      xs = [1, 2, 3, 4]
      ys = xs[::-1]
      alpha = [0.1, 0.7, 0.3, 0.2]
      data = {"x": xs, "y": ys, "alpha": alpha}
      path = Path([data], vdims="alpha").opts(alpha="alpha")
      msg = 'ValueError: Mapping a dimension to the "alpha" style'
      with pytest.raises(AbbreviatedException, match=msg):
          mpl_renderer.get_plot(path)
  
imports: import numpy
  import pytest
  from holoviews.core import NdOverlay
  from holoviews.core.options import AbbreviatedException
  from holoviews.core.spaces import HoloMap
  from holoviews.element import Contours, Path, Polygons
  from .test_plot import TestMPLPlot, mpl_renderer
label_desc: Use image node_id 2 for calling the TestPathPlot obj's underlying member method code with example usage: obj.test_path_continuously_varying_alpha_op() without return types