PHPUnit

<?php
declare(strict_types=1);
use PHPUnit\Framework\TestCase;
class StackTest extends TestCase
{
    public function testPushAndPop(): void
    {
        $stack = array();
        $this->assertEquals(0, count($stack));
        array_push($stack, 'foo');
        $this->assertEquals('foo', $stack[count($stack)-1]);
        $this->assertEquals(1, count($stack));
        $this->assertEquals('foo', array_pop($stack));
        $this->assertEquals(0, count($stack));
    }
}