public function testAddRemove()
{
$item1 = 'item 1';
$item2 = 'item 2';
$item3 = 'item 3';
$items = [$item1, $item2];
$stack = new Stack();
$stack->push($item1);
$this->assertEquals(1, $stack->size());
$this->assertEquals($item1, $stack->pop());
$this->assertEquals(0, $stack->size());
$stack->pushAll($items);
$this->assertEquals(2, $stack->size());
$stack->push($item3);
$this->assertEquals(3, $stack->size());
}
