Stack<Integer> stack = new ArrayStack<Integer>();
for (int i = 0; i<4; i++) stack.push(i);
assert stack.toString().equals("[0, 1, 2, 3]");
int top = stack.pop();
assert top==3 && stack.toString().equals("[0, 1, 2]");
Stack<Integer> reverse = Stacks.reverse(stack);
assert stack.empty();
assert reverse.toString().equals("[2, 1, 0]");
