code: def test_heatmap_custom_string_tooltip_hover(self):
      tooltips = "<div><h1>Test</h1></div>"
      custom_hover = HoverTool(tooltips=tooltips)
      hm = HeatMap(
          [(1, 1, 1), (2, 2, 0)],
          kdims=["x with space", "y with $pecial symbol"],
      )
      hm = hm.opts(tools=[custom_hover])
      plot = bokeh_renderer.get_plot(hm)
      hover = plot.handles["hover"]
      self.assertEqual(hover.tooltips, tooltips)
      self.assertEqual(
          hover.renderers, [plot.handles["glyph_renderer"]]
      )
  
file_path: holoviews/holoviews/tests/plotting/bokeh/test_heatmapplot.py
imports: import numpy
  from bokeh.models import FactorRange, HoverTool, Range1d
  from holoviews.element import HeatMap, Image, Points
  from .test_plot import TestBokehPlot, bokeh_renderer
label_desc: Use image node_id 2 for calling the TestHeatMapPlot obj's underlying member method code with example usage: obj.test_heatmap_custom_string_tooltip_hover() without return types