diff --git a/core/modules/ckeditor5/tests/src/FunctionalJavascript/CKEditor5AllowedTagsTest.php b/core/modules/ckeditor5/tests/src/FunctionalJavascript/CKEditor5AllowedTagsTest.php
index 07a26cc22112c8c8d00fc0e790afc89b2a92172c..540f54ada5152788667c56e97adad6452853b9da 100644
--- a/core/modules/ckeditor5/tests/src/FunctionalJavascript/CKEditor5AllowedTagsTest.php
+++ b/core/modules/ckeditor5/tests/src/FunctionalJavascript/CKEditor5AllowedTagsTest.php
@@ -457,7 +457,7 @@ public function testFullHtml() {
     // Add a node with text rendered via the Plain Text format.
     $this->drupalGet('node/add');
     $page->fillField('title[0][value]', 'My test content');
-    $page->fillField('body[0][value]', '<p><a style="color:#ff0000;" foo="bar" hreflang="en" href="https://example.com"><abbr title="National Aeronautics and Space Administration">NASA</abbr> is an acronym.</a></p>');
+    $page->fillField('body[0][value]', '<foo bar="baz">⬅️✌️➡️</foo><p><a style="color:#ff0000;" foo="bar" hreflang="en" href="https://example.com"><abbr title="National Aeronautics and Space Administration">NASA</abbr> is an acronym.</a></p>');
     $page->pressButton('Save');
 
     // Configure Full HTML text format to use CKEditor 5.
@@ -480,7 +480,7 @@ public function testFullHtml() {
 
     // But note that the `style` attribute was stripped by
     // \Drupal\editor\EditorXssFilter\Standard.
-    $assert_session->responseContains('<p><a foo="bar" hreflang="en" href="https://example.com"><abbr title="National Aeronautics and Space Administration">NASA</abbr> is an acronym.</a></p>');
+    $assert_session->responseContains('<foo bar="baz">⬅️✌️➡️</foo><p><a foo="bar" hreflang="en" href="https://example.com"><abbr title="National Aeronautics and Space Administration">NASA</abbr> is an acronym.</a></p>');
 
     // Ensure attributes are retained after enabling link plugin.
     $this->drupalGet('admin/config/content/formats/manage/full_html');
@@ -514,8 +514,8 @@ public function testFullHtml() {
     $page->pressButton('Save');
 
     // The `style` and foo` attributes should have been removed, as should the
-    // `<abbr>` tag.
-    $assert_session->responseContains('<p><a href="https://example.com" hreflang="en">NASA is an acronym.</a></p>');
+    // `<abbr>` and `<foo>` tags.
+    $assert_session->responseContains('<p>⬅️✌️➡️</p><p><a href="https://example.com" hreflang="en">NASA is an acronym.</a></p>');
   }
 
 }