diff --git a/core/modules/comment/src/Tests/CommentPreviewTest.php b/core/modules/comment/src/Tests/CommentPreviewTest.php
index 2353d95..5a589e5 100644
--- a/core/modules/comment/src/Tests/CommentPreviewTest.php
+++ b/core/modules/comment/src/Tests/CommentPreviewTest.php
@@ -45,6 +45,7 @@ function testCommentPreview() {
     $this->drupalPostForm('node/' . $this->node->id(), $edit, t('Preview'));
     $this->assertEscaped($this->webUser->getDisplayName());
 
+    \Drupal::service('module_installer')->install(['user_hooks_test']);
     \Drupal::state()->set('user_hooks_test_user_format_name_alter_safe', TRUE);
     $this->drupalPostForm('node/' . $this->node->id(), $edit, t('Preview'));
     $this->assertTrue($this->webUser->getDisplayName() instanceof MarkupInterface, 'Username is marked safe');
diff --git a/core/modules/search/src/Tests/SearchExactTest.php b/core/modules/search/src/Tests/SearchExactTest.php
index 92e8e86..792a315 100644
--- a/core/modules/search/src/Tests/SearchExactTest.php
+++ b/core/modules/search/src/Tests/SearchExactTest.php
@@ -62,7 +62,7 @@ function testExactQuery() {
 
     $edit = array('keys' => 'Druplicon');
     $this->drupalPostForm('search/node', $edit, t('Search'));
-    $this->assertText($user->getDisplayNameTruncated(), 'Basic page node displays author name when post settings are on.');
+    $this->assertEscaped($user->getDisplayNameTruncated(), 'Basic page node displays author name when post settings are on.');
     $this->assertText(format_date($node->getChangedTime(), 'short'), 'Basic page node displays post date when post settings are on.');
 
     // Check that with post settings turned off the user and changed date
diff --git a/core/modules/user/src/Entity/User.php b/core/modules/user/src/Entity/User.php
index 5de385c..f54f23d 100644
--- a/core/modules/user/src/Entity/User.php
+++ b/core/modules/user/src/Entity/User.php
@@ -383,7 +383,7 @@ public function getDisplayName() {
   public function getDisplayNameTruncated() {
     $name = $this->getDisplayName();
     if (Unicode::strlen($name) > 20) {
-      $name = Unicode::truncate($name, 15, FALSE, TRUE);
+      $name = Unicode::truncate((string) $name, 15, FALSE, TRUE);
     }
     return $name;
   }
diff --git a/core/modules/user/src/Tests/UserAdminTest.php b/core/modules/user/src/Tests/UserAdminTest.php
index bd2a12d..ed88f91 100644
--- a/core/modules/user/src/Tests/UserAdminTest.php
+++ b/core/modules/user/src/Tests/UserAdminTest.php
@@ -178,7 +178,7 @@ function testNotificationEmailAddress() {
     $edit['mail'] = $edit['name'] . '@example.com';
     $this->drupalPostForm('user/register', $edit, t('Create new account'));
     $user = user_load_by_name($edit['name']);
-    $subject = 'Account details for ' . $user->getDisplayName() . ' at ' . $system->get('name') . ' (pending admin approval)';
+    $subject = strip_tags('Account details for ' . $user->getDisplayName() . ' at ' . $system->get('name') . ' (pending admin approval)');
     // Ensure that admin notification mail is sent to the configured
     // Notification Email address.
     $admin_mail = $this->drupalGetMails(array(