code: def test_len(self):
      file_path = os.path.join(self.resource_path, "orca/data/csv")
      data_shard = bigdl.orca.data.pandas.read_csv(file_path)
      assert len(data_shard) == 14
      assert len(data_shard["ID"]) == 14
      with self.assertRaises(Exception) as context:
          len(data_shard["abc"])
      self.assertTrue(
          "Invalid key for this XShards" in str(context.exception)
      )
  
      def to_dict(df):
          return {
              "ID": df["ID"].to_numpy(),
              "location": df["location"].to_numpy(),
          }
  
      data_shard = data_shard.transform_shard(to_dict)
      assert len(data_shard["ID"]) == 14
      assert len(data_shard) == 4
      with self.assertRaises(Exception) as context:
          len(data_shard["abc"])
      self.assertTrue(
          "Invalid key for this XShards" in str(context.exception)
      )
  
      def to_number(d):
          return 4
  
      data_shard = data_shard.transform_shard(to_number)
      assert len(data_shard) == 2
      with self.assertRaises(Exception) as context:
          len(data_shard["abc"])
      self.assertTrue(
          "No selection operation available for this XShards"
          in str(context.exception)
      )
  
imports: import os.path
  import pytest
  from unittest import TestCase
  import bigdl.orca.data
  import bigdl.orca.data.pandas
  from bigdl.orca.data import SharedValue
  from bigdl.dllib.nncontext import *
  from bigdl.orca.data.transformer import *
  from bigdl.orca import init_orca_context
label_desc: Use image node_id 7 for calling the TestSparkXShards obj's underlying member method code with example usage: obj.test_len() and returns: dict, int