public class SignEvents implements Listener {
    private final JavaPlugin plugin;

    public SignEvents(JavaPlugin plugin) {
        this.plugin = plugin;
    }

    @EventHandler
    public void onPlayerInteract(PlayerInteractEvent e) {
        if (e.getClickedBlock() == null || !(e.getClickedBlock().getState() instanceof Sign)) {
            return;
        }

        Sign sign = (Sign) e.getClickedBlock().getState();
        String text = sign.getSide(Side.FRONT).getLine(0);
        
        if (text.equalsIgnoreCase("test")) {
            BukkitTask task = new BukkitRunnable() {

                @Override
                public void run() {
                    Inventory inv = e.getPlayer().getInventory();
                    final ItemStack testItem = new ItemStack(Material.DIAMOND_BLOCK, 10);
                    inv.clear();
                    inv.addItem(new ItemStack(Material.DIAMOND_BLOCK, 60));
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException exception) {
                        throw new RuntimeException(exception);
                    }

                    inv.addItem(testItem);

                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException exception) {
                        throw new RuntimeException(exception);
                    }
                    inv.removeItem(testItem);
                }
            }.runTaskTimer(this.plugin, 5 * 20L, 5 * 20L);
        }
    }
}