public void ToString_should_return_XX()
        {
            // arrange.
            const string ipAddress     = "10.1.1.10";
            const int    port          = 53;
            string       toStringValue = $"{ipAddress}:{port} (Udp: 512)";

            // Act.
            NameServer ns = new NameServer(IPAddress.Parse(ipAddress));

            // Assert.
            Assert.AreEqual(toStringValue, ns.ToString());
        }