code: def testPermalinkWithCustomClass(self):
      self.assertMarkdownRenders(
          "# Header",
          '<h1 id="header">'  # noqa
          "Header"  # noqa
          '<a class="custom" href="#header" title="Permanent link">&para;</a>'  # noqa
          "</h1>",  # noqa
          extensions=[
              TocExtension(permalink=True, permalink_class="custom")
          ],
      )
  
imports: from markdown.test_tools import TestCase
  from markdown.extensions.toc import TocExtension
  from markdown.extensions.nl2br import Nl2BrExtension
label_desc: Use image node_id 18 for calling the TestTOC obj's underlying member method code with example usage: obj.testPermalinkWithCustomClass() without return types