diff --git a/core/modules/simpletest/src/BrowserTestBase.php b/core/modules/simpletest/src/BrowserTestBase.php
index 6cba2e0..05a29fe 100644
--- a/core/modules/simpletest/src/BrowserTestBase.php
+++ b/core/modules/simpletest/src/BrowserTestBase.php
@@ -239,7 +239,9 @@ protected function setUp() {
     // coverage against.
     $base_url = getenv('SIMPLETEST_BASE_URL');
     if (!$base_url) {
-      throw new \InvalidArgumentException('You must provide a SIMPLETEST_BASE_URL environment variable to run PHPUnit based functional tests.');
+      $this->markTestSkipped(
+        'You must provide a SIMPLETEST_BASE_URL environment variable to run some PHPUnit based functional tests.'
+      );
     }
 
     // Setup $_SERVER variable.