code: def test_main(self):
      fa = FieldArray("x", [1, 2, 3, 4, 5])
      assert len(fa) == 5
      fa.append(6)
      assert len(fa) == 6
  
      assert fa[-1] == 6
      assert fa[0] == 1
      fa[-1] = 60
      assert fa[-1] == 60
  
      assert fa.get(0) == 1
      assert isinstance(fa.get([0, 1, 2]), np.ndarray) == True
      assert list(fa.get([0, 1, 2])) == [1, 2, 3]
  
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 1 for calling the TestFieldArray obj's underlying member method code with example usage: obj.test_main() without return types