Is there any way to make a tests for asynchronous functions in php?

one text

I'm trying to understand asynchronous function in PHP. I'm using spatie async package for this. I want to know, how can I check whether my code is working asynchrony or not?

I'm tried this code but every time I got same order in output.

use Spatie\Async\Pool;

$pool = Pool::create();

$nums = [1, 2, 3, 4, 5];

foreach ($nums as $num) {
    $pool->add( function () use($num) {
        $numSqr = $num * $num;
        
        return $numSqr;
    })->then( function ($numSqr) {
        echo $numSqr . '<br>';
    });
}

$pool->wait();

Output:

Source