A dummy/simple singleton to test it.

MySingleton.php

<?php

/**
 * Class MySingleton.
 */
class MySingleton
{
    private static $instance;

    private function __construct() {}

    /**
     * @return \MySingleton
     */
    public static function getInstance()
    {
        if (!self::$instance) {
            self::$instance = new self();
        }

        return self::$instance;
    }
}

$singleton1 = MySingleton::getInstance();
$singleton = MySingleton::getInstance();

var_dump($singleton);
var_dump($singleton1);
var_dump($singleton1 === $singleton);