BackendChainTest.php

<?php

namespace Drupal\KernelTests\Core\Cache;

use Drupal\Core\Cache\BackendChain;
use Drupal\Core\Cache\MemoryBackend;

/**
 * Unit test of the backend chain using the generic cache unit test base.
 *
 * @group Cache
 */
class BackendChainTest extends GenericCacheBackendUnitTestBase {
    protected function createCacheBackend($bin) {
        $chain = new BackendChain();
        // We need to create some various backends in the chain.
        $chain->appendBackend(new MemoryBackend())
            ->prependBackend(new MemoryBackend())
            ->appendBackend(new MemoryBackend());
        \Drupal::service('cache_tags.invalidator')->addInvalidator($chain);
        return $chain;
    }

}