code: def test_base64_roundtrip(self) -> None:
      for s in [
          "",
          "a",
          "ab",
          "abc",
          "abcd",
          "abcde",
          "abcdef",
          "abcdefg",
          "abcdefgh",
          "abcdefghi",
          "abcdefghijklmnopqrstuvwxyz",
      ]:
          assert s == _b64_to_utf8(_base64_encode(s))
  
imports: from __future__ import annotations
  import pytest
  import calendar
  import codecs
  import datetime
  import json
  import random
  from unittest.mock import MagicMock, Mock, patch
  from bokeh.util.token import _TOKEN_ZLIB_KEY, _base64_decode, _base64_encode, _get_sysrandom, _reseed_if_needed, _signature, check_token_signature, generate_jwt_token, generate_secret_key, generate_session_id, get_session_id, get_token_payload
  from tests.support.util.env import envset
  import bokeh.util.token
label_desc: Use image node_id 1 for calling the TestSessionId obj's underlying member method code with example usage: obj.test_base64_roundtrip() without return types