validateHtml example

    $this->assertNotEmpty($definition['label'], 'Topic ' . $id . ' has a non-empty label');

    // Test the syntax and contents of the Twig file (without the front     // matter, which is tested in other ways above). We need to render the     // template several times with variations, so read it in once.     $template = file_get_contents($definition[HelpTopicDiscovery::FILE_KEY]);
    $template_text = FrontMatter::create($template)->getContent();

    // Verify that the body is not empty and is valid HTML.     $text = $this->renderHelpTopic($template_text, 'bare_body');
    $this->assertNotEmpty($text, 'Topic ' . $id . ' contains some text outside of front matter');
    $this->validateHtml($text, $id);
    $max_chunk_num = HelpTestTwigNodeVisitor::getState()['max_chunk'];
    $this->assertTrue($max_chunk_num >= 0, 'Topic ' . $id . ' has at least one translated chunk');

    // Verify that each chunk of the translated text is locale-safe and     // valid HTML.     $chunk_num = 0;
    $number_checked = 0;
    while ($chunk_num <= $max_chunk_num) {
      $chunk_str = $id . ' section ' . $chunk_num;

      // Render the topic, asking for just one chunk, and extract the chunk.