code: def test_get_item_error(self):
      with pytest.raises(RuntimeError):
          ds = DataSet({"x": [[1, 2, 3, 4]] * 10, "y": [[5, 6]] * 10})
          _ = ds[40:]
  
      with pytest.raises(KeyError):
          ds = DataSet({"x": [[1, 2, 3, 4]] * 10, "y": [[5, 6]] * 10})
          _ = ds["kom"]
  
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 7 for calling the TestDataSetMethods obj's underlying member method code with example usage: obj.test_get_item_error() without return types