LibTest/collection/DoubleLinkedQueueEntry/previousEntry_A01_t02.dart

// Copyright (c) 2016, 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.

// @dart = 2.9

/// @assertion previousEntry() → DoubleLinkedQueueEntry<E>
/// Returns the previous entry or [null] if there is none.
/// @description Checks that nextEntry() returns the next element
/// @author sgrekhov@unipro.ru

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

main() {
  DoubleLinkedQueue queue = new DoubleLinkedQueue();
  queue.add(1);
  queue.add(2);
  queue.add(3);

  Expect.equals(2, queue.lastEntry().previousEntry().element);
  Expect.equals(1, queue.lastEntry().previousEntry().previousEntry().element);
  Expect.isNull(queue.firstEntry().previousEntry());
}