diff --git a/core/modules/simpletest/src/TestDiscovery.php b/core/modules/simpletest/src/TestDiscovery.php
index f71027d..a4d4f3a 100644
--- a/core/modules/simpletest/src/TestDiscovery.php
+++ b/core/modules/simpletest/src/TestDiscovery.php
@@ -191,7 +191,7 @@ public function getTestClasses($extension = NULL) {
     // Allow modules extending core tests to disable originals.
     \Drupal::moduleHandler()->alter('simpletest', $list);
 
-    if (!isset($extension)) {
+    if (!isset($extension) && FALSE) {
       if ($this->cacheBackend) {
         $this->cacheBackend->set('simpletest:discovery:classes', $list);
       }
@@ -358,7 +358,8 @@ public static function getTestInfo($classname, $doc_comment = NULL) {
    */
   public static function parseTestClassSummary($doc_comment) {
     // Normalize line endings.
-    $doc_comment = preg_replace('/\r\n|\r/', '\n', $doc_comment);
+    $doc_comment = str_replace('\r\n', '\n', $doc_comment);
+    $doc_comment = str_replace('\r', '\n', $doc_comment);
     // Strip leading and trailing doc block lines.
     $doc_comment = substr($doc_comment, 4, -4);