code: def test_stable_dir(self):
      assert util._stable_dir_identifier("my_dir", "*") == "my_dir+foo"
  
imports: import tempfile
  import unittest
  from unittest.mock import MagicMock, mock_open, patch
  from streamlit.watcher import util
label_desc: Use image node_id 5 for calling the DirHelperTests obj's underlying member method code with example usage: obj.test_stable_dir() without return types