prependBackend example

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;
  }

}