.../KernelTests/Core/Common/DrupalSetMessageLoadsCssTest.php     | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/core/tests/Drupal/KernelTests/Core/Common/DrupalSetMessageLoadsCssTest.php b/core/tests/Drupal/KernelTests/Core/Common/DrupalSetMessageLoadsCssTest.php
index f592237..4fdced1 100644
--- a/core/tests/Drupal/KernelTests/Core/Common/DrupalSetMessageLoadsCssTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Common/DrupalSetMessageLoadsCssTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\KernelTests\Core\Common;
 
+use Drupal\Core\Url;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -17,9 +18,15 @@
 class DrupalSetMessageLoadsCssTest extends WebTestBase {
 
   /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['session_test'];
+
+  /**
    * Check that a page does not load message assets when unrequired.
    */
   public function testDrupalSetMessage() {
+    $this->drupalLogin($this->rootUser);
 
     // Test with aggregated CSS turned off.
     $config = $this->config('system.performance');
@@ -34,7 +41,7 @@ public function testDrupalSetMessage() {
     $this->assertNoRaw("core/themes/classy/css/components/messages.css", "Message CSS assets should not be loaded when not needed.");
 
     // Display a message.
-    drupal_set_message(t('A status message.'));
+    $this->drupalGet(Url::fromRoute('session_test.set_message'));
 
     // Get the frontpage.
     $this->drupalGet("<front>");