code: def test_drop(self):
      ds = DataSet(
          {"x": [[1, 2, 3, 4]] * 40, "y": [[5, 6], [7, 8, 9, 0]] * 20}
      )
      ds.drop(lambda ins: len(ins["y"]) < 3, inplace=True)
      assert len(ds) == 20
  
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 19 for calling the TestDataSetMethods obj's underlying member method code with example usage: obj.test_drop() without return types