@NullUnmarked
public class SynchronizedQueueTest extends TestCase {

  protected Queue<String> create() {
    TestQueue<String> inner = new TestQueue<>();
    Queue<String> outer = Synchronized.queue(inner, inner.mutex);
    outer.add("foo"); // necessary because we try to remove elements later on
    return outer;
  }

  private static final class TestQueue<E> implements Queue<E> {
    private final Queue<E> delegate = new LinkedList<>();