code: def test_contains(self):
      ds = DataSet({"x": [[1, 2, 3, 4]] * 40, "y": [[5, 6]] * 40})
      assert ("x" in ds) == True
      assert ("y" in ds) == True
      assert ("z" in ds) == 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 20 for calling the TestDataSetMethods obj's underlying member method code with example usage: obj.test_contains() without return types