code: def test_idxmapping_nested_update(self):
      data1 = [(0, "a"), (1, "b")]
      data2 = [(2, "c"), (3, "d")]
      data3 = [(2, "e"), (3, "f")]
  
      ndmap1 = MultiDimensionalMapping(data1, kdims=[self.dim1])
      ndmap2 = MultiDimensionalMapping(data2, kdims=[self.dim1])
      ndmap3 = MultiDimensionalMapping(data3, kdims=[self.dim1])
  
      ndmap_list = [(0.5, ndmap1), (1.5, ndmap2)]
      nested_ndmap = MultiDimensionalMapping(
          ndmap_list, kdims=[self.dim2]
      )
      nested_ndmap[(0.5,)].update(dict([(0, "c"), (1, "d")]))
      self.assertEqual(list(nested_ndmap[0.5].values()), ["c", "d"])
  
      nested_ndmap[1.5] = ndmap3
      self.assertEqual(list(nested_ndmap[1.5].values()), ["e", "f"])
  
imports: import numpy
  from holoviews import Dataset, HoloMap
  from holoviews.core import Dimension
  from holoviews.core.ndmapping import MultiDimensionalMapping, NdMapping, UniformNdMapping
  from holoviews.core.overlay import Overlay
  from holoviews.element import Curve
  from holoviews.element.comparison import ComparisonTestCase
label_desc: Use image node_id 11 for calling the NdIndexableMappingTest obj's underlying member method code with example usage: obj.test_idxmapping_nested_update() without return types