private void VerifyState(ConcurrentDeque <int> deque, long expectedCount, long expectedSum)
{
//Assert
Assert.Equal(expectedCount, deque.Count);
Assert.Equal(expectedSum, deque.LongSum());
//test internal state
//traverse the deque in both directions
Assert.Equal(expectedCount, deque.TraverseLeftRight().LongCount());
Assert.Equal(expectedCount, deque.TraverseRightLeft().LongCount());
}