function book_test_page_attachments(array &$page) {
$page['#cache']['tags'][] = 'book_test.debug_book_navigation_cache_context';
if (\Drupal::state()->get('book_test.debug_book_navigation_cache_context', FALSE)) {
function book_test_page_attachments(array &$page) {
$page['#cache']['tags'][] = 'book_test.debug_book_navigation_cache_context';
if (\Drupal::state()->get('book_test.debug_book_navigation_cache_context', FALSE)) {