diff --git a/core/tests/TestSuites/TestSuiteBase.php b/core/tests/TestSuites/TestSuiteBase.php
index e5925de..d7849db 100644
--- a/core/tests/TestSuites/TestSuiteBase.php
+++ b/core/tests/TestSuites/TestSuiteBase.php
@@ -42,9 +42,9 @@ protected function addTestsBySuiteNamespace($root, $suite_namespace) {
     // to this is Unit tests for historical reasons.
     if ($suite_namespace == 'Unit') {
       $tests = TestDiscovery::scanDirectory("Drupal\\Tests\\", "$root/core/tests/Drupal/Tests");
-      $tests = array_filter($tests, function ($test) use ($root) {
+      $tests = array_filter($tests, function ($test) {
         // The Listeners directory does not contain tests.
-        return !preg_match("@^$root/core/tests/Drupal/Tests/Listeners(/|$)@", dirname($test));
+        return !preg_match('/.+core.tests.Drupal.Tests.Listeners(?:.|$)/', dirname($test));
       });
       $this->addTestFiles($tests);
     }