test isset($array[0]) versus count

arraytest.php

<?php
    $a = [];
    
    $t = microtime(true);

    for ($i = 0; $i < 1000000; $i++) {
        $sl = isset($a[0]);
    }    

    $t1 = microtime(true);

    echo $t1 - $t . chr(10);

    $t = microtime(true);

    for ($i = 0; $i < 1000000; $i++) {
        $sl = count($a);
    }    

    $t1 = microtime(true);

    echo $t1 - $t;
    
// 0.050590991973877
// 0.1452898979187