Fix unit-tests

src/WireMock.Net/Http/PortUtil.cs

@@ -0,0 +1,34 @@
+using System.Net;
+using System.Net.Sockets;
+
+namespace WireMock.Http
+{
+    /// <summary>
+    /// The ports.
+    /// </summary>
+    public static class PortUtil
+    {
+        /// <summary>
+        /// The find free TCP port.
+        /// </summary>
+        /// <returns>
+        /// The <see cref="int"/>.
+        /// </returns>
+        /// <remarks>see http://stackoverflow.com/questions/138043/find-the-next-tcp-port-in-net.</remarks>
+        public static int FindFreeTcpPort()
+        {
+            TcpListener tcpListener = null;
+            try
+            {
+                tcpListener = new TcpListener(IPAddress.Loopback, 0);
+                tcpListener.Start();
+
+                return ((IPEndPoint)tcpListener.LocalEndpoint).Port;
+            }
+            finally
+            {
+                tcpListener?.Stop();
+            }
+        }
+    }
+}