code: def test_len(self):
      layout_map = distribution_lib.LayoutMap(self.device_mesh)
      self.assertLen(layout_map, 0)
  
      layout_map["dense/kernel"] = self.sharded_2d
      layout_map["dense/bias"] = self.sharded_1d
  
      self.assertLen(layout_map, 2)
  
imports: import os
  from unittest import mock
  import numpy
  import pytest
  import tensorflow
  from keras import backend
  from keras import testing
  from keras.backend import distribution_lib
  from keras.distribution import distribution_lib
label_desc: Use image node_id 5 for calling the LayoutMapTest obj's underlying member method code with example usage: obj.test_len() without return types