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