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()); }