code: def test_vectorfield_categorical_color_op(self):
      vectorfield = VectorField(
          [(0, 0, 0, 1, "A"), (0, 1, 0, 1, "B"), (0, 2, 0, 1, "C")],
          vdims=["A", "M", "color"],
      ).opts(color="color")
      plot = bokeh_renderer.get_plot(vectorfield)
      cds = plot.handles["cds"]
      glyph = plot.handles["glyph"]
      cmapper = plot.handles["color_color_mapper"]
      self.assertTrue(cmapper, CategoricalColorMapper)
      self.assertEqual(cmapper.factors, ["A", "B", "C"])
      self.assertEqual(
          cds.data["color"],
          np.array(["A", "B", "C", "A", "B", "C", "A", "B", "C"]),
      )
      self.assertEqual(
          property_to_dict(glyph.line_color),
          {"field": "color", "transform": cmapper},
      )
  
file_path: holoviews/holoviews/tests/plotting/bokeh/test_vectorfieldplot.py
imports: import numpy
  from holoviews.element import VectorField
  from holoviews.plotting.bokeh.util import property_to_dict
  from ..utils import ParamLogStream
  from .test_plot import TestBokehPlot, bokeh_renderer
label_desc: Use image node_id 3 for calling the TestVectorFieldPlot obj's underlying member method code with example usage: obj.test_vectorfield_categorical_color_op() without return types