diff -u b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxTest.php
--- b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxTest.php
@@ -173,20 +173,20 @@
     // processed correctly.
     $test_cases['pre_wrapped_whitespace'] = [
       'pre-wrapped-whitespace',
-      '<div class="pre-wrapped-whitespace processed">pre-wrapped-whitespace</div>',
+      " <div class=\"pre-wrapped-whitespace processed\">pre-wrapped-whitespace</div>\n",
     ];
     // Test that not wrapped response data (text node) is inserted wrapped and
     // all top-level node elements (context) are processed correctly.
     $test_cases['not_wrapped'] = [
       'not-wrapped',
-      '<span class="processed">not-wrapped</span>',
+      'not-wrapped',
     ];
     // Test that not wrapped response data (text node and comment node) is
     // inserted wrapped and all top-level node elements
     // (context) are processed correctly.
     $test_cases['comment_string_not_wrapped'] = [
       'comment-string-not-wrapped',
-      '<span class="processed"><!-- COMMENT -->comment-string-not-wrapped</span>',
+      '<!-- COMMENT -->comment-string-not-wrapped',
     ];
     // Test that top-level comments (which are not lead by text nodes) are
     // inserted without wrapper.
@@ -198,7 +198,7 @@
     // is inserted correctly.
     $test_cases['mixed'] = [
       'mixed',
-      '<div class="processed"> foo <!-- COMMENT -->  foo bar<div class="a class"><p>some string</p></div> additional not wrapped strings, <!-- ANOTHER COMMENT --> <p>final string</p></div>',
+      ' foo <!-- COMMENT -->  foo bar<div class="a class processed"><p>some string</p></div> additional not wrapped strings, <!-- ANOTHER COMMENT --> <p class="processed">final string</p>',
     ];
     // Test that when the response has only top-level node elements, they
     // are processed properly without extra wrapping.
@@ -210,7 +210,7 @@
     // there are multiple top-level nodes.
     $test_cases['top_level_only_pre_whitespace'] = [
       'top-level-only-pre-whitespace',
-      '<div class="processed">element #1</div><div class="processed">element #2</div>',
+      ' <div class="processed">element #1</div><div class="processed">element #2</div> ',
     ];
     // Test when there are whitespaces between top-level divs.
     $test_cases['top_level_only_middle_whitespace-div'] = [