code: def test_get_item(self):
      file_path = os.path.join(self.resource_path, "orca/data/json")
      data_shard = bigdl.orca.data.pandas.read_json(
          file_path, orient="columns", lines=True
      )
      selected_shard = data_shard["value"]
      assert data_shard.is_cached(), "data_shard should be cached"
      assert (
          not selected_shard.is_cached()
      ), "selected_shard should not be cached"
      data1 = data_shard.collect()
      data2 = selected_shard.collect()
      assert (
          data1[0]["value"].values[0] == data2[0][0]
      ), "value should be same"
      assert (
          data1[1]["value"].values[0] == data2[1][0]
      ), "value should be same"
      with self.assertRaises(Exception) as context:
          len(data_shard["abc"])
      self.assertTrue(
          "Invalid key for this XShards" in str(context.exception)
      )
  
file_path: BigDL/python/orca/test/bigdl/orca/data/test_pandas_backend.py
imports: import os.path
  import shutil
  import pytest
  from unittest import TestCase
  import bigdl.orca.data
  import bigdl.orca.data.pandas
  from bigdl.orca import OrcaContext
  from bigdl.dllib.nncontext import *
label_desc: Use image node_id 8 for calling the TestXShardsPandasBackend obj's underlying member method code with example usage: obj.test_get_item() without return types