code: def test_load(self):
      corpus = PlainTextCorpus()
      corpus.load(self.plaintext_folder)
      self.assertEqual(4, len(corpus.documents))
  
file_path: underthesea/tests/corpus/test_plaintext.py
imports: import os
  import shutil
  from os import listdir
  from unittest import TestCase
  from os.path import join
  import sys
  from underthesea.corpus import PlainTextCorpus
label_desc: Use image node_id 3 for calling the TestPlainTextCorpus obj's underlying member method code with example usage: obj.test_load() without return types