code: def test_has_field(self):
      ds = DataSet({"x": [[1, 2, 3, 4]] * 40, "y": [[5, 6]] * 40})
      assert ds.has_field("x") == True
      assert ds.has_field("z") == False
  
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 11 for calling the TestDataSetMethods obj's underlying member method code with example usage: obj.test_has_field() without return types