--- /dev/null
+<?php
+
+namespace Drupal\system\Tests\System;
+
+use Drupal\Component\Utility\SafeMarkup;
+use Drupal\simpletest\WebTestBase;
+use Drupal\user\RoleInterface;
+
+/**
+ * Tests page not found functionality, including custom 404 pages.
+ *
+ * @group system
+ */
+class PageNotFoundTest extends WebTestBase {
+
+ /**
+ * Modules to enable.
+ *
+ * @var array
+ */
+ public static $modules = ['system_test'];
+
+ protected $adminUser;
+
+ protected function setUp() {
+ parent::setUp();
+
+ // Create an administrative user.
+ $this->adminUser = $this->drupalCreateUser(['administer site configuration', 'link to any page']);
+ $this->adminUser->roles[] = 'administrator';
+ $this->adminUser->save();
+
+ user_role_grant_permissions(RoleInterface::ANONYMOUS_ID, ['access user profiles']);
+ user_role_grant_permissions(RoleInterface::AUTHENTICATED_ID, ['access user profiles']);
+ }
+
+ public function testPageNotFound() {
+ $this->drupalLogin($this->adminUser);
+ $this->drupalGet($this->randomMachineName(10));
+ $this->assertText(t('Page not found'), 'Found the default 404 page');
+
+ // Set a custom 404 page without a starting slash.
+ $edit = [
+ 'site_404' => 'user/' . $this->adminUser->id(),
+ ];
+ $this->drupalPostForm('admin/config/system/site-information', $edit, t('Save configuration'));
+ $this->assertRaw(SafeMarkup::format("The path '%path' has to start with a slash.", ['%path' => $edit['site_404']]));
+
+ // Use a custom 404 page.
+ $edit = [
+ 'site_404' => '/user/' . $this->adminUser->id(),
+ ];
+ $this->drupalPostForm('admin/config/system/site-information', $edit, t('Save configuration'));
+
+ $this->drupalGet($this->randomMachineName(10));
+ $this->assertText($this->adminUser->getUsername(), 'Found the custom 404 page');
+ }
+
+ /**
+ * Tests that an inaccessible custom 404 page falls back to the default.
+ */
+ public function testPageNotFoundCustomPageWithAccessDenied() {
+ // Sets up a 404 page not accessible by the anonymous user.
+ $this->config('system.site')->set('page.404', '/system-test/custom-4xx')->save();
+
+ $this->drupalGet('/this-path-does-not-exist');
+ $this->assertNoText('Admin-only 4xx response');
+ $this->assertText('The requested page could not be found.');
+ $this->assertResponse(404);
+ // Verify the access cacheability metadata for custom 404 is bubbled.
+ $this->assertCacheContext('user.roles');
+
+ $this->drupalLogin($this->adminUser);
+ $this->drupalGet('/this-path-does-not-exist');
+ $this->assertText('Admin-only 4xx response');
+ $this->assertNoText('The requested page could not be found.');
+ $this->assertResponse(404);
+ // Verify the access cacheability metadata for custom 404 is bubbled.
+ $this->assertCacheContext('user.roles');
+ }
+
+}