diff --git a/core/modules/simpletest/src/TestDiscovery.php b/core/modules/simpletest/src/TestDiscovery.php
index a4d4f3a..87d3d3b 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($extension) && FALSE) {
+    if (!isset($extension)) {
       if ($this->cacheBackend) {
         $this->cacheBackend->set('simpletest:discovery:classes', $list);
       }