code: def test_idxmapping_key_len_check(self):
      try:
          MultiDimensionalMapping(initial_items=self.init_item_odict)
          raise AssertionError("Invalid key length check failed.")
      except KeyError:
          pass
  
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 10 for calling the NdIndexableMappingTest obj's underlying member method code with example usage: obj.test_idxmapping_key_len_check() without return types