#3487874: Only use localStorage after user interaction.

Closes #3487874

core/tests/Drupal/FunctionalJavascriptTests/Theme/OliveroAvoidStorageUsingTest.php

+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\FunctionalJavascriptTests\Theme;
+
+use Drupal\FunctionalJavascriptTests\WebDriverTestBase;
+
+/**
+ * Tests usage of localStorage.
+ *
+ * @group olivero
+ */
+final class OliveroAvoidStorageUsingTest extends WebDriverTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'node'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'olivero';
+
+  /**
+   * Tests use of localStorage.
+   */
+  public function testStorageUsing(): void {
+    $this->drupalGet('<front>');
+    // Check if initial no storage item is written.
+    $this->assertJsCondition("localStorage.getItem('Drupal.olivero.stickyHeaderState') === null", 10000, 'Written not strictly necessary Drupal.olivero.stickyHeaderState to localStorage without consent.');
+
+    // Resize and scroll to show stickyHeaderToggleButton.
+    $session = $this->getSession();
+    $session->resizeWindow(1280, 1024);
+    $session->executeScript('window.scrollTo(0, 500);');
+
+    // Click stickyHeaderToggleButton.
+    $this->getSession()->getPage()->find('css', '.sticky-header-toggle')->click();
+
+    // Test if localStorage is set now.
+    $this->assertJsCondition("localStorage.getItem('Drupal.olivero.stickyHeaderState') !== null");
+
+    // Click stickyHeaderToggleButton again.
+    $this->getSession()->getPage()->find('css', '.sticky-header-toggle')->click();
+
+    // Storage item should be removed now.
+    $this->assertJsCondition("localStorage.getItem('Drupal.olivero.stickyHeaderState') === null", 10000, 'Storage item Drupal.olivero.stickyHeaderState should be removed.');
+
+  }
+
+}