TestCommand.java

package commands;

import guis.TestGui;
import org.bukkit.command.Command;
import org.bukkit.command.CommandExecutor;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.jetbrains.annotations.NotNull;

public class TestCommand implements CommandExecutor {
    @Override
    public boolean onCommand(@NotNull CommandSender commandSender, @NotNull Command command, @NotNull String s, @NotNull String[] strings) {

        if (commandSender instanceof Player) {
            Player player = (Player) commandSender;
            TestGui test = new TestGui();
            test.openTestInventory(player);
            System.out.println("Gui should have opened.");


        }

        return false;
    }
}