diff --git a/core/modules/system/lib/Drupal/system/Tests/Common/AttributesUnitTest.php b/core/modules/system/lib/Drupal/system/Tests/Common/AttributesUnitTest.php
index 6910f7ad61f6fe3653e85207ca271625ffed3390..0e51b1ebf931529afe7e4ee8c256d44b0ad088b2 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Common/AttributesUnitTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Common/AttributesUnitTest.php
@@ -29,6 +29,27 @@ function testDrupalAttributes() {
     // Verify that special characters are HTML encoded.
     $this->assertIdentical((string) new Attribute(array('title' => '&"\'<>')), ' title="&amp;&quot;&#039;&lt;&gt;"', 'HTML encode attribute values.');
 
+    // Verify that decimal NCR characters are preserved.
+    $this->assertIdentical((string) new Attribute(array('title' => '&#931;')), ' title="&#931;"', 'Decimal NCR attribute values are preserved.');
+
+    // Verify that HTML encoded decimal NCR characters are preserved.
+    $this->assertIdentical((string) new Attribute(array('title' => '&amp;#931;')), ' title="&amp;#931;"', 'HTML Encoded decimal NCR attribute values are preserved.');
+
+    // Verify that hexadecimal NCR characters are preserved.
+    $this->assertIdentical((string) new Attribute(array('title' => '&#x03A3;')), ' title="&#x03A3;"', 'Hexadecimal NCR attribute values are preserved.');
+
+    // Verify that HTML encoded hexadecimal NCR characters are preserved.
+    $this->assertIdentical((string) new Attribute(array('title' => '&amp;#x03A3;')), ' title="&amp;#x03A3;"', 'HTML Encoded hexadecimal NCR attribute values are preserved.');
+
+    // Verify that named characters are preserved.
+    $this->assertIdentical((string) new Attribute(array('title' => '&reg;')), ' title="&reg;"', 'Named character entity attribute values are preserved.');
+
+    // Verify that HTML encoded named characters are preserved.
+    $this->assertIdentical((string) new Attribute(array('title' => '&amp;reg;')), ' title="&amp;reg;"', 'HTML Encoded named character entity attribute values are preserved.');
+
+    // Verify that iconic Unicode characters are preserved.
+    $this->assertIdentical((string) new Attribute(array('title' => '©')), ' title="©"', 'Iconic Unicode character attribute values are preserved.');
+
     // Verify multi-value attributes are concatenated with spaces.
     $attributes = array('class' => array('first', 'last'));
     $this->assertIdentical((string) new Attribute(array('class' => array('first', 'last'))), ' class="first last"', 'Concatenate multi-value attributes.');