diff --git a/core/tests/Drupal/Tests/Component/Transliteration/PhpTransliterationTest.php b/core/tests/Drupal/Tests/Component/Transliteration/PhpTransliterationTest.php
index 8bf5748..965ede5 100644
--- a/core/tests/Drupal/Tests/Component/Transliteration/PhpTransliterationTest.php
+++ b/core/tests/Drupal/Tests/Component/Transliteration/PhpTransliterationTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\Tests\Transliteration;
 
 use Drupal\Component\Transliteration\PHPTransliteration;
+use Drupal\Component\Utility\Random;
 use Drupal\Tests\UnitTestCase;
 
 /**
@@ -51,7 +52,7 @@ public function testPHPTransliteration($langcode, $original, $expected) {
    */
   public static function providerTestPHPTransliteration() {
 
-    $random = self::randomName(10);
+    $random = Random::String(10);
     // Make some strings with two, three, and four-byte characters for testing.
     // Note that the 3-byte character is overridden by the 'kg' language.
     $two_byte = 'Ä Ö Ü Å Ø äöüåøhello';
@@ -98,6 +99,8 @@ public static function providerTestPHPTransliteration() {
       // Test strings in some other languages.
       // Turkish, provided by drupal.org user Kartagis.
       array('tr', 'Abayı serdiler bize. Söyleyeceğim yüzlerine. Sanırım hepimiz aynı şeyi düşünüyoruz.', 'Abayi serdiler bize. Soyleyecegim yuzlerine. Sanirim hepimiz ayni seyi dusunuyoruz.'),
+      // Illegal/unknown unicode.
+      array('en', chr(0xF8) . chr(0x80) . chr(0x80) . chr(0x80) . chr(0x80), '?'),
     );
   }