code: def test_dirfiles_sorts_files_and_ignores_hidden(self):
      dirfiles = util._dirfiles(self._test_dir.name, "*")
      filename_prefixes = [f[:2] for f in dirfiles.split("+")]
      assert filename_prefixes == ["01", "02", "03", "04"]
  
imports: import tempfile
  import unittest
  from unittest.mock import MagicMock, mock_open, patch
  from streamlit.watcher import util
label_desc: Use image node_id 3 for calling the DirHelperTests obj's underlying member method code with example usage: obj.test_dirfiles_sorts_files_and_ignores_hidden() without return types