code: def test_idxmapping_add_dimension(self):
      ndmap = MultiDimensionalMapping(
          self.init_items_1D_list, kdims=[self.dim1]
      )
      ndmap2d = ndmap.add_dimension(self.dim2, 0, 0.5)
  
      self.assertEqual(list(ndmap2d.keys()), [(0.5, 1), (0.5, 5)])
      self.assertEqual(ndmap2d.kdims, [self.dim2, self.dim1])
  
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 27 for calling the NdIndexableMappingTest obj's underlying member method code with example usage: obj.test_idxmapping_add_dimension() without return types