trait BookTestTrait in Drupal 8

trait BookTestTrait {

  /**
   * A book node.
   *
   * @var \Drupal\node\NodeInterface
   */
  protected $book;

  /**
   * A user with permission to create and edit books.
   *
   * @var \Drupal\Core\Session\AccountInterface
   */
  protected $bookAuthor;

  /**
   * Creates a new book with a page hierarchy.
   *
   * @param array $edit
   *   (optional) Field data in an associative array. Changes the current input
   *   fields (where possible) to the values indicated. Defaults to an empty
   *   array.
   *
   * @return \Drupal\node\NodeInterface[]
   */
  public function createBook($edit = []) {

    // Create new book.
    $this
      ->drupalLogin($this->bookAuthor);
    $this->book = $this
      ->createBookNode('new', NULL, $edit);
    $book = $this->book;

    /*
     * Add page hierarchy to book.
     * Book
     *  |- Node 0
     *   |- Node 1
     *   |- Node 2
     *  |- Node 3
     *  |- Node 4
     */
    $nodes = [];

    // Node 0.
    $nodes[] = $this
      ->createBookNode($book
      ->id(), NULL, $edit);

    // Node 1.
    $nodes[] = $this
      ->createBookNode($book
      ->id(), $nodes[0]->book['nid'], $edit);

    // Node 2.
    $nodes[] = $this
      ->createBookNode($book
      ->id(), $nodes[0]->book['nid'], $edit);

    // Node 3.
    $nodes[] = $this
      ->createBookNode($book
      ->id(), NULL, $edit);

    // Node 4.
    $nodes[] = $this
      ->createBookNode($book
      ->id(), NULL, $edit);
    $this
      ->drupalLogout();
    return $nodes;
  }

  /**
   * Checks the outline of sub-pages; previous, up, and next.
   *
   * Also checks the printer friendly version of the outline.
   *
   * @param \Drupal\Core\Entity\EntityInterface $node
   *   Node to check.
   * @param $nodes
   *   Nodes that should be in outline.
   * @param $previous
   *   Previous link node.
   * @param $up
   *   Up link node.
   * @param $next
   *   Next link node.
   * @param array $breadcrumb
   *   The nodes that should be displayed in the breadcrumb.
   */
  public function checkBookNode(EntityInterface $node, $nodes, $previous, $up, $next, array $breadcrumb) {

    // $number does not use drupal_static as it should not be reset
    // since it uniquely identifies each call to checkBookNode().
    static $number = 0;
    $this
      ->drupalGet('node/' . $node
      ->id());

    // Check outline structure.
    if ($nodes !== NULL) {
      $this
        ->assertPattern($this
        ->generateOutlinePattern($nodes));
    }
    else {
      $this
        ->pass(new FormattableMarkup('Node %number does not have outline.', [
        '%number' => $number,
      ]));
    }

    // Check previous, up, and next links.
    if ($previous) {

      /** @var \Drupal\Core\Url $url */
      $url = $previous
        ->toUrl();
      $url
        ->setOptions([
        'attributes' => [
          'rel' => [
            'prev',
          ],
          'title' => t('Go to previous page'),
        ],
      ]);
      $text = new FormattableMarkup('<b>‹</b> @label', [
        '@label' => $previous
          ->label(),
      ]);
      $this
        ->assertRaw(Link::fromTextAndUrl($text, $url)
        ->toString(), 'Previous page link found.');
    }
    if ($up) {

      /** @var \Drupal\Core\Url $url */
      $url = $up
        ->toUrl();
      $url
        ->setOptions([
        'attributes' => [
          'title' => t('Go to parent page'),
        ],
      ]);
      $this
        ->assertRaw(Link::fromTextAndUrl('Up', $url)
        ->toString(), 'Up page link found.');
    }
    if ($next) {

      /** @var \Drupal\Core\Url $url */
      $url = $next
        ->toUrl();
      $url
        ->setOptions([
        'attributes' => [
          'rel' => [
            'next',
          ],
          'title' => t('Go to next page'),
        ],
      ]);
      $text = new FormattableMarkup('@label <b>›</b>', [
        '@label' => $next
          ->label(),
      ]);
      $this
        ->assertRaw(Link::fromTextAndUrl($text, $url)
        ->toString(), 'Next page link found.');
    }

    // Compute the expected breadcrumb.
    $expected_breadcrumb = [];
    $expected_breadcrumb[] = Url::fromRoute('<front>')
      ->toString();
    foreach ($breadcrumb as $a_node) {
      $expected_breadcrumb[] = $a_node
        ->toUrl()
        ->toString();
    }

    // Fetch links in the current breadcrumb.
    $links = $this
      ->xpath('//nav[@class="breadcrumb"]/ol/li/a');
    $got_breadcrumb = [];
    foreach ($links as $link) {
      $got_breadcrumb[] = $link
        ->getAttribute('href');
    }

    // Compare expected and got breadcrumbs.
    $this
      ->assertIdentical($expected_breadcrumb, $got_breadcrumb, 'The breadcrumb is correctly displayed on the page.');

    // Check printer friendly version.
    $this
      ->drupalGet('book/export/html/' . $node
      ->id());
    $this
      ->assertText($node
      ->label(), 'Printer friendly title found.');
    $this
      ->assertRaw($node->body->processed, 'Printer friendly body found.');
    $number++;
  }

  /**
   * Creates a regular expression to check for the sub-nodes in the outline.
   *
   * @param array $nodes
   *   An array of nodes to check in outline.
   *
   * @return string
   *   A regular expression that locates sub-nodes of the outline.
   */
  public function generateOutlinePattern($nodes) {
    $outline = '';
    foreach ($nodes as $node) {
      $outline .= '(node\\/' . $node
        ->id() . ')(.*?)(' . $node
        ->label() . ')(.*?)';
    }
    return '/<nav id="book-navigation-' . $this->book
      ->id() . '"(.*?)<ul(.*?)' . $outline . '<\\/ul>/s';
  }

  /**
   * Creates a book node.
   *
   * @param int|string $book_nid
   *   A book node ID or set to 'new' to create a new book.
   * @param int|null $parent
   *   (optional) Parent book reference ID. Defaults to NULL.
   * @param array $edit
   *   (optional) Field data in an associative array. Changes the current input
   *   fields (where possible) to the values indicated. Defaults to an empty
   *   array.
   *
   * @return \Drupal\node\NodeInterface
   *   The created node.
   */
  public function createBookNode($book_nid, $parent = NULL, $edit = []) {

    // $number does not use drupal_static as it should not be reset
    // since it uniquely identifies each call to createBookNode().
    // Used to ensure that when sorted nodes stay in same order.
    static $number = 0;
    $edit['title[0][value]'] = str_pad($number, 2, '0', STR_PAD_LEFT) . ' - SimpleTest test node ' . $this
      ->randomMachineName(10);
    $edit['body[0][value]'] = 'SimpleTest test body ' . $this
      ->randomMachineName(32) . ' ' . $this
      ->randomMachineName(32);
    $edit['book[bid]'] = $book_nid;
    if ($parent !== NULL) {
      $this
        ->drupalPostForm('node/add/book', $edit, t('Change book (update list of parents)'));
      $edit['book[pid]'] = $parent;
      $this
        ->drupalPostForm(NULL, $edit, t('Save'));

      // Make sure the parent was flagged as having children.
      $parent_node = \Drupal::entityTypeManager()
        ->getStorage('node')
        ->loadUnchanged($parent);
      $this
        ->assertFalse(empty($parent_node->book['has_children']), 'Parent node is marked as having children');
    }
    else {
      $this
        ->drupalPostForm('node/add/book', $edit, t('Save'));
    }

    // Check to make sure the book node was created.
    $node = $this
      ->drupalGetNodeByTitle($edit['title[0][value]']);
    $this
      ->assertNotNull($node === FALSE ? NULL : $node, 'Book node found in database.');
    $number++;
    return $node;
  }

}