<?php

$host = 'db' ;
$user = 'devuser';
$password = 'devpass';
$db = 'test_db';

$conn = new mysqli($host, $user, $password, $db);
if($conn->connect_error)
{
    echo "Cos poszlo nie tak...: " . $conn->connect_error;
}
echo "Polaczono z baza danych";
?>