FormatStringTest.php

<?php

namespace Drupal\KernelTests\Core\Bootstrap;

use Drupal\Component\Render\FormattableMarkup;
use Drupal\KernelTests\KernelTestBase;

/**
 * Tests deprecated behavior of format_string.
 *
 * @group Bootstrap
 * @group legacy
 */
class FormatStringTest extends KernelTestBase {
    
    /**
     * Tests error triggering on format_string.
     *
     * @expectedDeprecation format_string() is deprecated in drupal:8.0.0 and is removed from drupal:9.0.0. Use \Drupal\Component\Render\FormattableMarkup instead. See https://www.drupal.org/node/2302363
     */
    public function testFormatString() {
        $markup = \format_string("Test", []);
        $this->assertInstanceOf(FormattableMarkup::class, $markup);
    }

}