BreadcrumbTest.php

<?php

namespace Drupal\Tests\Core\Breadcrumb;

use Drupal\Core\Breadcrumb\Breadcrumb;
use Drupal\Core\Link;
use Drupal\Core\Url;
use Drupal\Tests\UnitTestCase;

/**
 * @coversDefaultClass \Drupal\Core\Breadcrumb\Breadcrumb
 * @group Breadcrumb
 */
class BreadcrumbTest extends UnitTestCase {
    
    /**
     * @covers ::setLinks
     */
    public function testSetLinks() {
        $breadcrumb = new Breadcrumb();
        $breadcrumb->setLinks([
            new Link('Home', Url::fromRoute('<front>')),
        ]);
        $this->expectException(\LogicException::class);
        $this->expectExceptionMessage('Once breadcrumb links are set, only additional breadcrumb links can be added.');
        $breadcrumb->setLinks([
            new Link('None', Url::fromRoute('<none>')),
        ]);
    }

}