code: def test_single_hline(self):
      hline = HLine(3)
      state = self._get_plot_state(hline)
  
      shapes = state["layout"]["shapes"]
      self.assertEqual(len(shapes), 1)
      self.assert_hline(shapes[0], 3)
  
imports: import numpy
  from holoviews.element import Bounds, Box, HLine, Path, Rectangles, Segments, Tiles, VLine
  from .test_plot import TestPlotlyPlot
label_desc: Use image node_id 4 for calling the TestVLineHLine obj's underlying member method code with example usage: obj.test_single_hline() without return types