[bcl] Fix a few hardcoded socket ports in tests (#5471)

* [System] Fix a few hardcoded socket ports in tests

Those could've shown up as "address already in use" in CI.

* [System.Runtime.Remoting] Fix a few hardcoded socket ports in tests

Those could've shown up as "address already in use" in CI.

Additionally remove a copy of RemotingServicesTest.cs from corlib
which also exists in System.Runtime.Remoting in updated form.

* [System.ServiceModel] Fix a few hardcoded socket ports in tests

Those could've shown up as "address already in use" in CI.

* [System.Net.Http] Fix a few hardcoded socket ports in tests

Those could've shown up as "address already in use" in CI.

The additional "keep-alive" header in Send_Complete_NoContent() and
Send_Transfer_Encoding_Chunked() is because we were using the same
port for all tests before so other tests would clear the header.
This doesn't happen now that we use distinct test ports.

* [System.ServiceModel.Web] Fix a few hardcoded socket ports in tests

Those could've shown up as "address already in use" in CI.

4 files changed, 70 insertions, 71 deletions

diff --git a/mcs/class/System/Test/System.Net.Sockets/SocketTest.cs b/mcs/class/System/Test/System.Net.Sockets/SocketTest.cs
index 4bdfd61de26..5925388413a 100755
--- a/mcs/class/System/Test/System.Net.Sockets/SocketTest.cs
+++ b/mcs/class/System/Test/System.Net.Sockets/SocketTest.cs
@@ -30,9 +30,7 @@ namespace MonoTests.System.Net.Sockets
 	[TestFixture]
 	public class SocketTest
 	{
-		// note: also used in SocketCas tests
 		public const string BogusAddress = "192.168.244.244";
-		public const int BogusPort = 23483;
 
 		[Test]
 #if FEATURE_NO_BSD_SOCKETS
@@ -94,7 +92,7 @@ namespace MonoTests.System.Net.Sockets
 		public void BogusEndConnect ()
 		{
 			IPAddress ipOne = IPAddress.Parse (BogusAddress);
-			IPEndPoint ipEP = new IPEndPoint (ipOne, BogusPort);
+			IPEndPoint ipEP = new IPEndPoint (ipOne, NetworkHelpers.FindFreePort ());
 			Socket sock = new Socket (ipEP.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
 			IAsyncResult ar = sock.BeginConnect (ipEP, null, null);
 
@@ -501,8 +499,7 @@ namespace MonoTests.System.Net.Sockets
 			Socket sock = new Socket (AddressFamily.InterNetwork,
 						  SocketType.Stream,
 						  ProtocolType.Tcp);
-			IPEndPoint ep = new IPEndPoint (IPAddress.Loopback,
-							BogusPort);
+			IPEndPoint ep = NetworkHelpers.LocalEphemeralEndPoint ();
 			
 			SocketError_event.Reset ();
 
@@ -745,8 +742,7 @@ namespace MonoTests.System.Net.Sockets
 			Socket sock = new Socket (AddressFamily.InterNetwork,
 						  SocketType.Stream,
 						  ProtocolType.Tcp);
-			IPEndPoint ep = new IPEndPoint (IPAddress.Loopback,
-							BogusPort);
+			IPEndPoint ep = NetworkHelpers.LocalEphemeralEndPoint ();
 			
 			Assert.AreEqual (false, sock.IsBound, "IsBoundTcp #1");
 			
@@ -780,8 +776,7 @@ namespace MonoTests.System.Net.Sockets
 			Socket sock = new Socket (AddressFamily.InterNetwork,
 						  SocketType.Dgram,
 						  ProtocolType.Udp);
-			IPEndPoint ep = new IPEndPoint (IPAddress.Loopback,
-							BogusPort);
+			IPEndPoint ep = NetworkHelpers.LocalEphemeralEndPoint ();
 			
 			Assert.AreEqual (false, sock.IsBound, "IsBoundUdp #1");
 			
@@ -1739,13 +1734,14 @@ namespace MonoTests.System.Net.Sockets
 		[Test]
 		public void BeginConnectAddressPortNull ()
 		{
+			var port = NetworkHelpers.FindFreePort ();
 			Socket sock = new Socket (AddressFamily.InterNetwork,
 						  SocketType.Stream,
 						  ProtocolType.Tcp);
 			IPAddress ip = null;
 
 			try {
-				sock.BeginConnect (ip, 1244, BCCallback,
+				sock.BeginConnect (ip, port, BCCallback,
 						   sock);
 				Assert.Fail ("BeginConnectAddressPortNull #1");
 			} catch (ArgumentNullException) {
@@ -1782,6 +1778,7 @@ namespace MonoTests.System.Net.Sockets
 		[ExpectedException (typeof(ObjectDisposedException))]
 		public void BeginConnectAddressPortClosed ()
 		{
+			var port = NetworkHelpers.FindFreePort ();
 			Socket sock = new Socket (AddressFamily.InterNetwork,
 						  SocketType.Stream,
 						  ProtocolType.Tcp);
@@ -1789,7 +1786,7 @@ namespace MonoTests.System.Net.Sockets
 			
 			sock.Close ();
 			
-			sock.BeginConnect (ip, 1244, BCCallback, sock);
+			sock.BeginConnect (ip, port, BCCallback, sock);
 		}
 		
 		[Test]
@@ -1911,13 +1908,14 @@ namespace MonoTests.System.Net.Sockets
 		[Test]
 		public void BeginConnectMultipleNull ()
 		{
+			var port = NetworkHelpers.FindFreePort ();
 			Socket sock = new Socket (AddressFamily.InterNetwork,
 						  SocketType.Stream,
 						  ProtocolType.Tcp);
 			IPAddress[] ips = null;
 			
 			try {
-				sock.BeginConnect (ips, 1246, BCCallback,
+				sock.BeginConnect (ips, port, BCCallback,
 						   sock);
 				Assert.Fail ("BeginConnectMultipleNull #1");
 			} catch (ArgumentNullException) {
@@ -1961,6 +1959,7 @@ namespace MonoTests.System.Net.Sockets
 		[ExpectedException (typeof(ObjectDisposedException))]
 		public void BeginConnectMultipleClosed ()
 		{
+			var port = NetworkHelpers.FindFreePort ();
 			Socket sock = new Socket (AddressFamily.InterNetwork,
 						  SocketType.Stream,
 						  ProtocolType.Tcp);
@@ -1973,7 +1972,7 @@ namespace MonoTests.System.Net.Sockets
 			
 			sock.Close ();
 			
-			sock.BeginConnect (ips, 1247, BCCallback, sock);
+			sock.BeginConnect (ips, port, BCCallback, sock);
 		}
 		
 		[Test]
@@ -2248,13 +2247,14 @@ namespace MonoTests.System.Net.Sockets
 		[Test]
 		public void ConnectAddressPortNull ()
 		{
+			var port = NetworkHelpers.FindFreePort ();
 			Socket sock = new Socket (AddressFamily.InterNetwork,
 						  SocketType.Stream,
 						  ProtocolType.Tcp);
 			IPAddress ip = null;
 
 			try {
-				sock.Connect (ip, 1249);
+				sock.Connect (ip, port);
 				Assert.Fail ("ConnectAddressPortNull #1");
 			} catch (ArgumentNullException) {
 			} finally {
@@ -2290,6 +2290,7 @@ namespace MonoTests.System.Net.Sockets
 		[ExpectedException (typeof(ObjectDisposedException))]
 		public void ConnectAddressPortClosed ()
 		{
+			var port = NetworkHelpers.FindFreePort ();
 			Socket sock = new Socket (AddressFamily.InterNetwork,
 						  SocketType.Stream,
 						  ProtocolType.Tcp);
@@ -2297,7 +2298,7 @@ namespace MonoTests.System.Net.Sockets
 			
 			sock.Close ();
 			
-			sock.Connect (ip, 1250);
+			sock.Connect (ip, port);
 		}
 		
 		[Test]
@@ -2397,13 +2398,14 @@ namespace MonoTests.System.Net.Sockets
 		[Test]
 		public void ConnectMultipleNull ()
 		{
+			var port = NetworkHelpers.FindFreePort ();
 			Socket sock = new Socket (AddressFamily.InterNetwork,
 						  SocketType.Stream,
 						  ProtocolType.Tcp);
 			IPAddress[] ips = null;
 			
 			try {
-				sock.Connect (ips, 1251);
+				sock.Connect (ips, port);
 				Assert.Fail ("ConnectMultipleNull #1");
 			} catch (ArgumentNullException) {
 			} finally {
@@ -2445,6 +2447,7 @@ namespace MonoTests.System.Net.Sockets
 		[ExpectedException (typeof(ObjectDisposedException))]
 		public void ConnectMultipleClosed ()
 		{
+			var port = NetworkHelpers.FindFreePort ();
 			Socket sock = new Socket (AddressFamily.InterNetwork,
 						  SocketType.Stream,
 						  ProtocolType.Tcp);
@@ -2457,7 +2460,7 @@ namespace MonoTests.System.Net.Sockets
 			
 			sock.Close ();
 			
-			sock.Connect (ips, 1252);
+			sock.Connect (ips, port);
 		}
 		
 		[Test]
@@ -4301,7 +4304,7 @@ namespace MonoTests.System.Net.Sockets
 				IPv6MulticastOption option = new IPv6MulticastOption (
 					IPAddress.Parse ("ff02::1"));
 
-				s.Bind (new IPEndPoint (IPAddress.IPv6Any, 1902));
+				s.Bind (new IPEndPoint (IPAddress.IPv6Any, 0));
 				s.SetSocketOption (SocketOptionLevel.IPv6, SocketOptionName.AddMembership,
 					option);
 				s.SetSocketOption (SocketOptionLevel.IPv6, SocketOptionName.DropMembership,
diff --git a/mcs/class/System/Test/System.Net.Sockets/TcpClientTest.cs b/mcs/class/System/Test/System.Net.Sockets/TcpClientTest.cs
index cefe3bebc59..d827ae4de36 100644
--- a/mcs/class/System/Test/System.Net.Sockets/TcpClientTest.cs
+++ b/mcs/class/System/Test/System.Net.Sockets/TcpClientTest.cs
@@ -155,7 +155,7 @@ namespace MonoTests.System.Net.Sockets
 			TcpClient client = new TcpClient ();
 			IPAddress[] ipAddresses = null;
 			
-			client.Connect (ipAddresses, 1234);
+			client.Connect (ipAddresses, NetworkHelpers.FindFreePort ());
 		}
 		
 		[Test]
@@ -170,7 +170,7 @@ namespace MonoTests.System.Net.Sockets
 			ipAddresses[0] = IPAddress.Any;
 			
 			try {
-				client.Connect (ipAddresses, 1234);
+				client.Connect (ipAddresses, NetworkHelpers.FindFreePort ());
 				Assert.Fail ("ConnectMultiAny #1");
 			} catch (SocketException ex) {
 				Assert.AreEqual (10049, ex.ErrorCode, "ConnectMultiAny #2");
@@ -191,7 +191,7 @@ namespace MonoTests.System.Net.Sockets
 			ipAddresses[0] = IPAddress.Loopback;
 			
 			try {
-				client.Connect (ipAddresses, 1234);
+				client.Connect (ipAddresses, NetworkHelpers.FindFreePort ());
 				Assert.Fail ("ConnectMultiRefused #1");
 			} catch (SocketException ex) {
 				Assert.AreEqual (10061, ex.ErrorCode, "ConnectMultiRefused #2");
diff --git a/mcs/class/System/Test/System.Net.Sockets/UdpClientTest.cs b/mcs/class/System/Test/System.Net.Sockets/UdpClientTest.cs
index 29ab8ef2ca6..1d2373b6215 100644
--- a/mcs/class/System/Test/System.Net.Sockets/UdpClientTest.cs
+++ b/mcs/class/System/Test/System.Net.Sockets/UdpClientTest.cs
@@ -13,6 +13,8 @@ using System.Threading.Tasks;
 
 using NUnit.Framework;
 
+using MonoTests.Helpers;
+
 namespace MonoTests.System.Net.Sockets {
 	[TestFixture]
 	public class UdpClientTest {
@@ -212,7 +214,7 @@ namespace MonoTests.System.Net.Sockets {
 			IPEndPoint localEP;
 			IPEndPoint clientEP;
 
-			clientEP = new IPEndPoint (IPAddress.Loopback, 8001);
+			clientEP = new IPEndPoint (IPAddress.Loopback, NetworkHelpers.FindFreePort ());
 			using (MyUdpClient client = new MyUdpClient (clientEP))
 			{
 				s = client.Client;
@@ -381,9 +383,7 @@ namespace MonoTests.System.Net.Sockets {
 			Socket s;
 			IPEndPoint localEP;
 
-			// Bug #5503
-			// UDP port 0 doesn't seem to be valid.
-			using (MyUdpClient client = new MyUdpClient ("127.0.0.1", 53))
+			using (MyUdpClient client = new MyUdpClient ("127.0.0.1", NetworkHelpers.FindFreePort ()))
 			{
 				s = client.Client;
 				Assert.IsNotNull (s, "#A:Client");
@@ -481,7 +481,7 @@ namespace MonoTests.System.Net.Sockets {
 			byte[] bytes = new byte[] {10, 11, 12, 13};
 
 			try {
-				client.Send (bytes, bytes.Length, new IPEndPoint (IPAddress.Broadcast, 1235));
+				client.Send (bytes, bytes.Length, new IPEndPoint (IPAddress.Broadcast, NetworkHelpers.FindFreePort ()));
 			} finally {
 				client.Close ();
 			}
@@ -495,7 +495,7 @@ namespace MonoTests.System.Net.Sockets {
 		{
 			IPAddress mcast_addr = IPAddress.Parse ("224.0.0.23");
 
-			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Any, 1234))) {
+			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Any, 0))) {
 				client.JoinMulticastGroup (mcast_addr);
 			}
 		}
@@ -511,7 +511,7 @@ namespace MonoTests.System.Net.Sockets {
 
 			IPAddress mcast_addr = IPAddress.Parse ("ff02::1");
 
-			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.IPv6Any, 1234))) {
+			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.IPv6Any, 0))) {
 				client.JoinMulticastGroup (mcast_addr);
 			}
 		}
@@ -522,7 +522,7 @@ namespace MonoTests.System.Net.Sockets {
 #endif
 		public void JoinMulticastGroup1_MulticastAddr_Null ()
 		{
-			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Loopback, 1234))) {
+			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Loopback, 0))) {
 				try {
 					client.JoinMulticastGroup ((IPAddress) null);
 					Assert.Fail ("#1");
@@ -543,7 +543,7 @@ namespace MonoTests.System.Net.Sockets {
 		{
 			IPAddress mcast_addr = null;
 
-			UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Loopback, 1234));
+			UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Loopback, 0));
 			client.Close ();
 			try {
 				client.JoinMulticastGroup (mcast_addr);
@@ -578,7 +578,7 @@ namespace MonoTests.System.Net.Sockets {
 		{
 			IPAddress mcast_addr = IPAddress.Parse ("224.0.0.23");
 
-			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Any, 1234))) {
+			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Any, 0))) {
 				try {
 					client.JoinMulticastGroup (0, mcast_addr);
 					Assert.Fail ("#1");
@@ -606,7 +606,7 @@ namespace MonoTests.System.Net.Sockets {
 
 			IPAddress mcast_addr = IPAddress.Parse ("ff02::1");
 
-			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.IPv6Any, 1234))) {
+			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.IPv6Any, 0))) {
 				client.JoinMulticastGroup (0, mcast_addr);
 			}
 		}
@@ -617,7 +617,7 @@ namespace MonoTests.System.Net.Sockets {
 #endif
 		public void JoinMulticastGroup2_MulticastAddr_Null ()
 		{
-			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Loopback, 1234))) {
+			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Loopback, 0))) {
 				try {
 					client.JoinMulticastGroup (0, (IPAddress) null);
 					Assert.Fail ("#1");
@@ -641,7 +641,7 @@ namespace MonoTests.System.Net.Sockets {
 
 			IPAddress mcast_addr = null;
 
-			UdpClient client = new UdpClient (new IPEndPoint (IPAddress.IPv6Any, 1234));
+			UdpClient client = new UdpClient (new IPEndPoint (IPAddress.IPv6Any, 0));
 			client.Close ();
 			try {
 				client.JoinMulticastGroup (0, mcast_addr);
@@ -676,11 +676,11 @@ namespace MonoTests.System.Net.Sockets {
 		{
 			IPAddress mcast_addr = IPAddress.Parse ("224.0.0.23");
 
-			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Any, 1234))) {
+			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Any, 0))) {
 				client.JoinMulticastGroup (mcast_addr, 0);
 			}
 
-			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Any, 1234))) {
+			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Any, 0))) {
 				client.JoinMulticastGroup (mcast_addr, 255);
 			}
 		}
@@ -696,11 +696,11 @@ namespace MonoTests.System.Net.Sockets {
 
 			IPAddress mcast_addr = IPAddress.Parse ("ff02::1");
 
-			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.IPv6Any, 1234))) {
+			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.IPv6Any, 0))) {
 				client.JoinMulticastGroup (mcast_addr, 0);
 			}
 
-			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.IPv6Any, 1234))) {
+			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.IPv6Any, 0))) {
 				client.JoinMulticastGroup (mcast_addr, 255);
 			}
 		}
@@ -711,7 +711,7 @@ namespace MonoTests.System.Net.Sockets {
 #endif
 		public void JoinMulticastGroup3_MulticastAddr_Null ()
 		{
-			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Loopback, 1234))) {
+			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Loopback, 0))) {
 				try {
 					client.JoinMulticastGroup ((IPAddress) null, int.MaxValue);
 					Assert.Fail ("#1");
@@ -732,7 +732,7 @@ namespace MonoTests.System.Net.Sockets {
 		{
 			IPAddress mcast_addr = null;
 
-			UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Any, 1234));
+			UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Any, 0));
 			client.Close ();
 			try {
 				client.JoinMulticastGroup (mcast_addr, 0);
@@ -768,7 +768,7 @@ namespace MonoTests.System.Net.Sockets {
 			IPAddress mcast_addr = IPAddress.Parse ("224.0.0.23");
 			IPAddress local_addr = IPAddress.Any;
 
-			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Any, 1234))) {
+			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Any, 0))) {
 				client.JoinMulticastGroup (mcast_addr, local_addr);
 			}
 		}
@@ -785,7 +785,7 @@ namespace MonoTests.System.Net.Sockets {
 			IPAddress mcast_addr = IPAddress.Parse ("ff02::1");
 			IPAddress local_addr = IPAddress.IPv6Any;
 
-			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.IPv6Any, 1234))) {
+			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.IPv6Any, 0))) {
 				try {
 					client.JoinMulticastGroup (mcast_addr, local_addr);
 					Assert.Fail ("#1");
@@ -810,7 +810,7 @@ namespace MonoTests.System.Net.Sockets {
 		{
 			IPAddress mcast_addr = IPAddress.Parse ("224.0.0.23");
 
-			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Loopback, 1234))) {
+			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Loopback, 0))) {
 				try {
 					client.JoinMulticastGroup (mcast_addr, (IPAddress) null);
 					Assert.Fail ("#1");
@@ -829,7 +829,7 @@ namespace MonoTests.System.Net.Sockets {
 #endif
 		public void JoinMulticastGroup4_MulticastAddr_Null ()
 		{
-			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Loopback, 1234))) {
+			using (UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Loopback, 0))) {
 				try {
 					client.JoinMulticastGroup ((IPAddress) null, IPAddress.Loopback);
 					Assert.Fail ("#1");
@@ -851,7 +851,7 @@ namespace MonoTests.System.Net.Sockets {
 			IPAddress mcast_addr = null;
 			IPAddress local_addr = null;
 
-			UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Any, 1234));
+			UdpClient client = new UdpClient (new IPEndPoint (IPAddress.Any, 0));
 			client.Close ();
 			try {
 				client.JoinMulticastGroup (mcast_addr, local_addr);
@@ -885,18 +885,7 @@ namespace MonoTests.System.Net.Sockets {
 #endif
 		public void CloseInReceive ()
 		{
-			UdpClient client = null;
-			var rnd = new Random ();
-			for (int i = 0, max = 5; i < max; i++) {
-				int port = rnd.Next (1025, 65534);
-				try {
-					client = new UdpClient (port);
-					break;
-				} catch (Exception) {
-					if (i == max - 1)
-						throw;
-				}
-			}
+			UdpClient client = new UdpClient (NetworkHelpers.FindFreePort ());
 
 			ManualResetEvent ready = new ManualResetEvent (false);
 			bool got_exc = false;
@@ -928,7 +917,7 @@ namespace MonoTests.System.Net.Sockets {
 #endif
 		public void JoinMulticastGroupWithLocal ()
 		{
-			UdpClient client = new UdpClient (9001);
+			UdpClient client = new UdpClient (0);
 			IPAddress mcast_addr = IPAddress.Parse ("224.0.0.24");
 			IPAddress local_addr = IPAddress.Any;
 
@@ -995,7 +984,7 @@ namespace MonoTests.System.Net.Sockets {
 			IPEndPoint ep = null;
 			foreach (IPAddress a in addresses) {
 				if (a.AddressFamily == AddressFamily.InterNetwork) {
-					ep = new IPEndPoint (a, 1236);
+					ep = new IPEndPoint (a, NetworkHelpers.FindFreePort ());
 					break;
 				}
 			}
@@ -1035,13 +1024,14 @@ namespace MonoTests.System.Net.Sockets {
 #endif
 		public void BeginReceive ()
 		{
-			UdpClient client = new UdpClient (1237);
+			var port = NetworkHelpers.FindFreePort ();
+			UdpClient client = new UdpClient (port);
 			
 			BRCalledBack.Reset ();
 			
 			client.BeginReceive (BRCallback, client);
 
-			IPEndPoint ep = new IPEndPoint (IPAddress.Loopback, 1237);
+			IPEndPoint ep = new IPEndPoint (IPAddress.Loopback, port);
 			byte[] send_bytes = new byte[] {10, 11, 12, 13};
 			client.Send (send_bytes, send_bytes.Length, ep);
 
@@ -1063,8 +1053,9 @@ namespace MonoTests.System.Net.Sockets {
 #endif
 		public void Available ()
 		{
-			using (UdpClient client = new UdpClient (1238)) {
-				IPEndPoint ep = new IPEndPoint (IPAddress.Loopback, 1238);
+			var port = NetworkHelpers.FindFreePort ();
+			using (UdpClient client = new UdpClient (port)) {
+				IPEndPoint ep = new IPEndPoint (IPAddress.Loopback, port);
 				byte[] bytes = new byte[] {10, 11, 12, 13};
 				
 				int res = client.Send (bytes, bytes.Length, ep);
@@ -1129,7 +1120,7 @@ namespace MonoTests.System.Net.Sockets {
 		[Category ("NotWorking")] // Not supported on Linux
 		public void ExclusiveAddressUseBound ()
 		{
-			UdpClient client = new UdpClient (1239);
+			UdpClient client = new UdpClient (0);
 
 			client.ExclusiveAddressUse = true;
 
@@ -1158,12 +1149,13 @@ namespace MonoTests.System.Net.Sockets {
 			if (!Socket.OSSupportsIPv6)
 				Assert.Ignore ("IPv6 not enabled.");
 
-			int PORT = 9997;
-			using(var udpClient = new UdpClient (PORT, AddressFamily.InterNetworkV6))
-			using(var udpClient2 = new UdpClient (PORT+1, AddressFamily.InterNetworkV6))
+			int port1 = NetworkHelpers.FindFreePort ();
+			int port2 = NetworkHelpers.FindFreePort ();
+			using(var udpClient = new UdpClient (port1, AddressFamily.InterNetworkV6))
+			using(var udpClient2 = new UdpClient (port2, AddressFamily.InterNetworkV6))
 			{
 				var dataSent = new byte [] {1,2,3};
-				udpClient2.SendAsync (dataSent, dataSent.Length, "::1", PORT);
+				udpClient2.SendAsync (dataSent, dataSent.Length, "::1", port1);
 
 				IPEndPoint endPoint = new IPEndPoint (IPAddress.IPv6Any, 0);
 				var data = udpClient.Receive (ref endPoint);
diff --git a/mcs/class/System/Test/System.Net/HttpListenerPrefixCollectionTest.cs b/mcs/class/System/Test/System.Net/HttpListenerPrefixCollectionTest.cs
index b09a8180eaf..20763df5802 100644
--- a/mcs/class/System/Test/System.Net/HttpListenerPrefixCollectionTest.cs
+++ b/mcs/class/System/Test/System.Net/HttpListenerPrefixCollectionTest.cs
@@ -31,6 +31,8 @@ using System.Net;
 using NUnit.Framework;
 using HLPC=System.Net.HttpListenerPrefixCollection;
 
+using MonoTests.Helpers;
+
 namespace MonoTests.System.Net {
 	[TestFixture]
 	public class HttpListenerPrefixCollectionTest {
@@ -68,10 +70,11 @@ namespace MonoTests.System.Net {
 #endif
 		public void AddOne ()
 		{
+			var port = NetworkHelpers.FindFreePort ();
 			HttpListener listener = new HttpListener ();
 			HLPC coll = listener.Prefixes;
 			listener.Start ();
-			coll.Add ("http://127.0.0.1:8181/");
+			coll.Add ($"http://127.0.0.1:{port}/");
 			Assert.AreEqual (1, coll.Count, "Count");
 			Assert.IsFalse (coll.IsReadOnly, "IsReadOnly");
 			Assert.IsFalse (coll.IsSynchronized, "IsSynchronized");
@@ -84,10 +87,11 @@ namespace MonoTests.System.Net {
 #endif
 		public void Duplicate ()
 		{
+			var port = NetworkHelpers.FindFreePort ();
 			HttpListener listener = new HttpListener ();
 			HLPC coll = listener.Prefixes;
-			coll.Add ("http://127.0.0.1:8181/");
-			coll.Add ("http://127.0.0.1:8181/");
+			coll.Add ($"http://127.0.0.1:{port}/");
+			coll.Add ($"http://127.0.0.1:{port}/");
 			listener.Start ();
 			Assert.AreEqual (1, coll.Count, "Count");
 			Assert.IsFalse (coll.IsReadOnly, "IsReadOnly");