<?php
    $files_dir = "./tests";
    $files_list = scandir($files_dir);
    echo '<ol>';
    foreach ($files_list as $value)
    {
        if ($value !='.' and $value !='..' )
        {
            echo '<li><a href="./tests'. $value.'">'.$value.'</a></li><br>';
        }
        else{}
    }
    echo '</ol>';
?>

$tests = [
  1 => ['name' => 'Test1', 'test' => '{test1}'],
  2 => ['name' => 'Test2', 'test' => '{test2}'],
  3 => ['name' => 'Test3', 'test' => '{test3}']
];

foreach ($tests as $id => $test)
  printf('<a href="test.php?id=%s>%s</a>', $key, $test['name']);

if(!isset($_GET['id']) || !isset($tests[$_GET['id']]))
  die('Invalid test id');
$test = $tests[$_GET['id']];
showTest($test['test']);

echo '<li><a href="./tests'. $value.'">'.$value.'</a></li><br>';

echo '<li><a href="test.php?id='. $value.'">'.$value.'</a></li><br>';

if(!isset($_GET['id']) || !file_exists('./tests/' .$_GET['id']))
  die('Invalid test id');
$test_file_name = $_GET['id'];
................