add StartThrowsWithUnboundPortTest

src/csharp/Grpc.Core.Tests/ServerTest.cs

@@ -32,6 +32,7 @@
 #endregion
 
 using System;
+using System.IO;
 using System.Linq;
 using Grpc.Core;
 using Grpc.Core.Internal;
@@ -80,6 +81,21 @@ namespace Grpc.Core.Tests
             server.ShutdownAsync().Wait();
         }
 
+        [Test]
+        public void StartThrowsWithUnboundPorts()
+        {
+            int twiceBoundPort = 9999;
+            Server server = new Server(new[] { new ChannelOption(ChannelOptions.SoReuseport, 0) })
+            {
+                Ports = {
+                    new ServerPort("localhost", twiceBoundPort, ServerCredentials.Insecure),
+                    new ServerPort("localhost", twiceBoundPort, ServerCredentials.Insecure)
+                }
+            };
+            Assert.Throws(typeof(IOException), () => server.Start());
+            server.ShutdownAsync().Wait();
+        }
+
         [Test]
         public void CannotModifyAfterStarted()
         {