code: def test_append(self):
      fa = FieldArray(
          "y", [[1.1, 2.2, 3.3, 4.4, 5.5], [1.0, 2.0, 3.0, 4.0, 5.0]]
      )
      fa.append([1.2, 2.3, 3.4, 4.5, 5.6])
      assert len(fa) == 3
      assert fa[2] == [1.2, 2.3, 3.4, 4.5, 5.6]
  
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 4 for calling the TestFieldArray obj's underlying member method code with example usage: obj.test_append() without return types