// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

/// @assertion final E single
/// Returns the single element in this.
/// @description Checks that the method returns the single element of the queue.
/// Checks that if this is empty or has more than one element throws a StateError.
/// @author kaigorodov

import "dart:collection";
import "../../../Utils/expect.dart";

main() {
  DoubleLinkedQueue queue = new DoubleLinkedQueue();
      
  Expect.throws(() { queue.single; }, (e) => e is StateError);
  
  queue.addFirst(1);
  Expect.isTrue(queue.first == 1);
  
  queue.addLast(2);
  Expect.throws(() { queue.single; }, (e) => e is StateError);
}