code: def test_build_header_with_east_asian_characters(self):
      header = build_header(
          "これは広い幅の文字だけで構成されたタイトルです",
          None,
          None,
          None,
          None,
          None,
      )
  
      self.assertEqual(
          header,
          (
              "これは広い幅の文字だけで構成されたタイトルです\n"
              "##############################################"
              "\n\n"
          ),
      )
  
imports: import os
  import re
  from posixpath import join
  from unittest.mock import patch
  from pelican.settings import DEFAULT_CONFIG
  from pelican.tests.support import mute, skipIfNoExecutable, temporary_folder, unittest, TestCaseWithCLocale
  from pelican.tools.pelican_import import blogger2fields, build_header, build_markdown_header, decode_wp_content, download_attachments, fields2pelican, get_attachments, tumblr2fields, wp2fields
  from pelican.utils import path_to_file_url, slugify
label_desc: Use image node_id 3 for calling the TestBuildHeader obj's underlying member method code with example usage: obj.test_build_header_with_east_asian_characters() without return types