TestUtilities.cs

using System.Net;
using System.Net.Sockets;

namespace DnsClientX.Tests {
    internal static class TestUtilities {
        public static int GetFreePort() {
            return GetFreeTcpPort();
        }

        public static int GetFreeTcpPort() {
            TcpListener listener = new TcpListener(IPAddress.Loopback, 0);
            listener.Start();
            int port = ((IPEndPoint)listener.LocalEndpoint).Port;
            listener.Stop();
            return port;
        }

        public static int GetFreeUdpPort() {
            using var socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
            socket.Bind(new IPEndPoint(IPAddress.Loopback, 0));
            return ((IPEndPoint)socket.LocalEndPoint!).Port;
        }
    }
}