class_docstr: Credentials Module Unittest class.
docstr: Test _verify_email.
code: def test_verify_email(self):
      """Test _verify_email."""
      self.assertTrue(_verify_email("user@domain.com").is_valid)
      self.assertTrue(_verify_email("").is_valid)
      self.assertFalse(_verify_email("missing_at_sign").is_valid)
  
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 1 for calling the CredentialsModulesTest obj's underlying member method code with example usage: obj.test_verify_email() without return types