Add test coverage

core/modules/path_alias/tests/src/Functional/SiteInformationFormAlterTest.php

+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\path_alias\Functional;
+
+use Drupal\node\NodeInterface;
+use Drupal\Tests\BrowserTestBase;
+use Drupal\Tests\Traits\Core\PathAliasTestTrait;
+
+/**
+ * Tests site information form alter functionality.
+ *
+ * @group path_alias
+ */
+class SiteInformationFormAlterTest extends BrowserTestBase {
+
+  use PathAliasTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['node', 'path_alias'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * The node that is created for testing.
+   */
+  protected NodeInterface $node;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Create admin user, log in admin user, and create a node type.
+    $this->drupalLogin($this->drupalCreateUser([
+      'access content',
+      'administer site configuration',
+    ]));
+    $this->drupalCreateContentType(['type' => 'page']);
+  }
+
+  /**
+   * Tests form alter.
+   */
+  public function testFormAlter(): void {
+    $node = $this->drupalCreateNode();
+    $this->createPathAlias('/node/' . $node->id(), '/foo');
+
+    // Configure site information.
+    $this->drupalGet('admin/config/system/site-information');
+    $this->submitForm([
+      'site_frontpage' => '/foo',
+      'site_403' => '/foo',
+      'site_404' => '/foo',
+    ], 'Save configuration');
+    $this->assertSession()->pageTextContains('The configuration options have been saved.');
+
+    // Check that the system paths has been saved.
+    $this->assertSame('/node/1', $this->config('system.site')->get('page.front'));
+    $this->assertSame('/node/1', $this->config('system.site')->get('page.403'));
+    $this->assertSame('/node/1', $this->config('system.site')->get('page.404'));
+
+    // Check that only the front page path is converted to an alias.
+    $page = $this->getSession()->getPage();
+    $this->assertSame('/foo', $page->findField('site_frontpage')->getValue());
+    $this->assertSame('/node/1', $page->findField('site_403')->getValue());
+    $this->assertSame('/node/1', $page->findField('site_404')->getValue());
+  }
+
+}