class AjaxMaintenanceModeTest

class AjaxMaintenanceModeTest extends WebDriverTestBase {
    use FieldUiTestTrait;
    use FileFieldCreationTrait;
    use TestFileCreationTrait;
    
    /**
     * An user with administration permissions.
     *
     * @var \Drupal\user\UserInterface
     */
    protected $adminUser;
    
    /**
     * {@inheritdoc}
     */
    protected static $modules = [
        'ajax_test',
    ];
    
    /**
     * {@inheritdoc}
     */
    protected $defaultTheme = 'stark';
    
    /**
     * {@inheritdoc}
     */
    protected function setUp() : void {
        parent::setUp();
        $this->adminUser = $this->drupalCreateUser([
            'access administration pages',
            'administer site configuration',
            'access site in maintenance mode',
        ]);
        $this->drupalLogin($this->adminUser);
    }
    
    /**
     * Tests maintenance message only appears once on an AJAX call.
     */
    public function testAjaxCallMaintenanceMode() : void {
        $page = $this->getSession()
            ->getPage();
        $assert_session = $this->assertSession();
        \Drupal::state()->set('system.maintenance_mode', TRUE);
        $this->drupalGet('ajax-test/insert-inline-wrapper');
        $assert_session->pageTextContains('Target inline');
        $page->clickLink('Link html pre-wrapped-div');
        $this->assertSession()
            ->assertWaitOnAjaxRequest();
        $this->assertSession()
            ->pageTextContainsOnce('Operating in maintenance mode');
    }

}