diff -u b/core/modules/book/src/BookManager.php b/core/modules/book/src/BookManager.php
--- b/core/modules/book/src/BookManager.php
+++ b/core/modules/book/src/BookManager.php
@@ -261,8 +261,8 @@
       }
       if (!$node->book['bid'] || $nid === 'new' || $node->book['original_bid'] === 0) {
         // The node is not currently in the hierarchy.
-            $options = [0 => $this->t('- None -')] + $options;
-        }
+        $options = [0 => $this->t('- None -')] + $options;
+      }
 
       // Add a drop-down to select the destination book.
       $form['book']['bid'] = [
diff -u b/core/modules/book/tests/src/Unit/BookManagerTest.php b/core/modules/book/tests/src/Unit/BookManagerTest.php
--- b/core/modules/book/tests/src/Unit/BookManagerTest.php
+++ b/core/modules/book/tests/src/Unit/BookManagerTest.php
@@ -56,7 +56,21 @@
   protected $bookOutlineStorage;
 
   /**
-   * The mocked form state
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    $this->entityTypeManager = $this->createMock(EntityTypeManagerInterface::class);
+    $this->translation = $this->getStringTranslationStub();
+    $this->configFactory = $this->getConfigFactoryStub([]);
+    $this->bookOutlineStorage = $this->createMock('Drupal\book\BookOutlineStorageInterface');
+    $this->renderer = $this->createMock('\Drupal\Core\Render\RendererInterface');
+    $this->bookManager = new BookManager($this->entityTypeManager, $this->translation, $this->configFactory, $this->bookOutlineStorage, $this->renderer);
+  }
+   */
+  protected $bookOutlineStorage;
+
+  /**
+   * The mocked form state.
    *
    * @var \Drupal\Core\Form\FormState
    */
@@ -70,7 +84,7 @@
   protected $node;
 
   /**
-   * The mocked User
+   * The mocked User.
    *
    * @var \Drupal\user\Entity\User
    */
@@ -79,7 +93,7 @@
   /**
    * {@inheritdoc}
    */
-  protected function setUp() {
+  protected function setUp(): void {
     $this->entityTypeManager = $this->createMock(EntityTypeManagerInterface::class);
     $book_id = [
       'nid' => 'new',
@@ -107,9 +121,9 @@
     $config = [
       'book.settings' => [
         'allowed_types' => [
-          'page'
-        ]
-      ]
+          'page',
+        ],
+      ],
     ];
     $this->configFactory = $this->getConfigFactoryStub($config);
     $this->bookOutlineStorage = $this->createMock('Drupal\book\BookOutlineStorageInterface');
@@ -117,20 +131,6 @@
     $container = new ContainerBuilder();
     $container->set('config.factory', $this->configFactory);
     \Drupal::setContainer($container);
-    $this->bookManager = new BookManager($this->entityTypeManager, $this->translation, $this->configFactory, $this->bookOutlineStorage, $this->renderer);
-  }
-   */
-  protected $bookOutlineStorage;
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp(): void {
-    $this->entityTypeManager = $this->createMock(EntityTypeManagerInterface::class);
-    $this->translation = $this->getStringTranslationStub();
-    $this->configFactory = $this->getConfigFactoryStub([]);
-    $this->bookOutlineStorage = $this->createMock('Drupal\book\BookOutlineStorageInterface');
-    $this->renderer = $this->createMock('\Drupal\Core\Render\RendererInterface');
     $this->languageManager = $this->createMock('Drupal\Core\Language\LanguageManagerInterface');
     $this->entityRepository = $this->createMock('Drupal\Core\Entity\EntityRepositoryInterface');
     $this->bookManager = new BookManager($this->entityTypeManager, $this->translation, $this->configFactory, $this->bookOutlineStorage, $this->renderer, $this->languageManager, $this->entityRepository);
@@ -194,21 +194,21 @@
     $this->node->expects($this->any())
       ->method('getType')
       ->willReturn('page');
-    $addform = $this->bookManager->addFormElements($form, $this->form_state, $this->node, $this->account);
-    $this->assertArrayHasKey('book', $addform);
+    $add_form = $this->bookManager->addFormElements($form, $this->form_state, $this->node, $this->account);
+    $this->assertArrayHasKey('book', $form);
   }
 
   /**
    * Testing the Book Outline form element in node add article form.
-   * When the Book setting is not enabled for the Content Type 'Article'
+   * When the Book setting is not enabled for the Content Type 'Article'.
    */
   public function testAddFormElementsNodeAddWithoutBook() {
     $form = [];
     $this->node->expects($this->any())
       ->method('getType')
-      ->willReturn('artilce');
-    $addform = $this->bookManager->addFormElements($form, $this->form_state, $this->node, $this->account);
-    $this->assertArrayNotHasKey('book', $addform);
+      ->willReturn('article');
+    $add_form = $this->bookManager->addFormElements($form, $this->form_state, $this->node, $this->account);
+    $this->assertArrayNotHasKey('book', $form);
   }
 
 }