Added the proper class

Closes #3298580

core/modules/system/tests/src/Functional/Form/ElementTest.php

@@ -19,7 +19,7 @@ class ElementTest extends BrowserTestBase {
    *
    * @var array
    */
-  protected static $modules = ['form_test'];
+  protected static $modules = ['form_test', 'inline_form_errors'];
 
   /**
    * {@inheritdoc}
@@ -189,11 +189,24 @@ public function testFormAutocomplete() {
 
   /**
    * Tests form element error messages.
+   *  @dataProvider themeDataProvider
    */
-  public function testFormElementErrors() {
+  public function testFormElementErrors(string $theme): void {
+    if ($theme) {
+      \Drupal::service('theme_installer')->install([$theme]);
+      $this->config('system.theme')
+        ->set('default', $theme)
+        ->save();
+    }
     $this->drupalGet('form_test/details-form');
     $this->submitForm([], 'Submit');
     $this->assertSession()->pageTextContains('I am an error on the details element.');
+
+    // Assert that the correct error class is used.
+    if ($theme) {
+      $this->assertSession()->elementExists('css', '.form-item__error-message');
+    }
+
   }
 
   /**
@@ -204,4 +217,17 @@ public function testDetailsSummaryAttributes() {
     $this->assertSession()->elementExists('css', 'summary[data-summary-attribute="test"]');
   }
 
+  /**
+   * Provide data for testFormElementErrors.
+   *
+   * @return array
+   *   An array of themes to test.
+   */
+  public static function themeDataProvider(): array {
+    return [
+      [''],
+      ['claro'],
+    ];
+  }
+
 }