--- /dev/null
+<?php
+
+namespace Drupal\Tests\system\Kernel\Render;
+
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests the Classy theme.
+ *
+ * @group Theme
+ */
+class ClassyTest extends KernelTestBase {
+
+ /**
+ * {@inheritdoc}
+ */
+ public static $modules = ['system', 'twig_theme_test'];
+
+ /**
+ * {@inheritdoc}
+ */
+ public function setUp() {
+ parent::setUp();
+
+ // Use the classy theme.
+ $this->container->get('theme_installer')->install(['classy']);
+ $this->container->get('config.factory')
+ ->getEditable('system.theme')
+ ->set('default', 'classy')
+ ->save();
+ // Clear the theme registry.
+ $this->container->set('theme.registry', NULL);
+
+ }
+
+ /**
+ * Test the classy theme.
+ */
+ public function testClassyTheme() {
+ drupal_set_message('An error occurred', 'error');
+ drupal_set_message('But then something nice happened');
+ $messages = [
+ '#type' => 'status_messages',
+ ];
+ $this->render($messages);
+ $this->assertNoText('custom-test-messages-class', 'The custom class attribute value added in the status messages preprocess function is not displayed as page content.');
+ }
+
+}