code: def test_md5_calculation_allow_nonexistent(self):
      md5 = util.calc_md5_with_blocking_retries(
          "hello", allow_nonexistent=True
      )
      self.assertEqual(md5, "5d41402abc4b2a76b9719d911017c592")
  
imports: import tempfile
  import unittest
  from unittest.mock import MagicMock, mock_open, patch
  from streamlit.watcher import util
label_desc: Use image node_id 4 for calling the UtilTest obj's underlying member method code with example usage: obj.test_md5_calculation_allow_nonexistent() without return types