code: def test_split(self):
      ds = DataSet({"x": [[1, 2, 3, 4]] * 10, "y": [[5, 6]] * 10})
      d1, d2 = ds.split(0.1)
      assert len(d2) == (len(ds) * 0.9)
      assert len(d1) == (len(ds) * 0.1)
  
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 22 for calling the TestDataSetMethods obj's underlying member method code with example usage: obj.test_split() without return types