class_docstr: Credentials Class Unittest class.
docstr: Test that saving a new Credential does not send an email if the email is invalid
code: def test_email_not_send(self, temp_dir):
      """
      Test that saving a new Credential does not send an email if the email is invalid
      """
  
      with requests_mock.mock() as m:
          m.post("https://api.segment.io/v1/t", status_code=200)
          creds: Credentials = Credentials.get_current()  # type: ignore
          creds._conf_file = str(Path(temp_dir.path) / "config.toml")
          creds.activation = _verify_email("some_email")
          creds.save()
          assert len(m.request_history) == 0
  
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 21 for calling the CredentialsClassTest obj's underlying member method code with example usage: obj.test_email_not_send(temp_dir) without return types