code: def test_save_load(self):
      ds = DataSet({"x": [[1, 2, 3, 4]] * 10, "y": [[5, 6]] * 10})
      ds.save("./my_ds.pkl")
      assert os.path.exists("./my_ds.pkl") == True
  
      ds_1 = DataSet.load("./my_ds.pkl")
      os.remove("my_ds.pkl")
  
imports: import os
  import pytest
  import numpy
  from fastNLP.core.dataset import DataSet, FieldArray, Instance, ApplyResultException
  from fastNLP import logger
label_desc: Use image node_id 24 for calling the TestDataSetMethods obj's underlying member method code with example usage: obj.test_save_load() without return types