class_docstr: Credentials Class Unittest class.
docstr: Test Credentials constructor runs twice.
code: def test_Credentials_constructor_runs_twice(self):
      """Test Credentials constructor runs twice."""
      Credentials._singleton = None
      Credentials()
      with pytest.raises(RuntimeError) as e:
          Credentials()
      self.assertEqual(
          str(e.value),
          "Credentials already initialized. Use .get_current() instead",
      )
  
imports: import os
  import textwrap
  import unittest
  from pathlib import Path
  from unittest.mock import MagicMock, call, mock_open, patch
  import pytest
  import requests_mock
  from testfixtures import tempdir
  from streamlit import file_util
  from streamlit.runtime.credentials import Credentials, _Activation, _verify_email, email_prompt
label_desc: Use image node_id 5 for calling the CredentialsClassTest obj's underlying member method code with example usage: obj.test_Credentials_constructor_runs_twice() without return types