code: def test_geom_union(self):
      rects = Rectangles([(0, 0, 1, 1), (1, 0, 2, 1)])
      geom = rects.geom(union=True)
      self.assertIsInstance(geom, Polygon)
      array = np.array(geom.exterior.coords)
      try:
          self.assertEqual(
              array,
              np.array(
                  [
                      [0, 0],
                      [0, 1],
                      [1, 1],
                      [2, 1],
                      [2, 0],
                      [1, 0],
                      [0, 0],
                  ]
              ),
          )
      except Exception:
          self.assertEqual(
              array,
              np.array(
                  [
                      [1, 0],
                      [0, 0],
                      [0, 1],
                      [1, 1],
                      [2, 1],
                      [2, 0],
                      [1, 0],
                  ]
              ),
          )
  
imports: import numpy
  from holoviews.element.comparison import ComparisonTestCase
  from shapely.geometry import GeometryCollection, Polygon, Point, LineString, LinearRing, MultiPolygon, MultiLineString, MultiPoint
  from geoviews.element import Rectangles, Path, Polygons, Points, Segments
label_desc: Use image node_id 4 for calling the TestRectangles obj's underlying member method code with example usage: obj.test_geom_union() without return types