Test project: Enable netcore3.1 testing, switch win64 Snap7 and use custom port.

- Add netcoreapp3.1 target framework, allowing this to run on linux and macos as well.
- Switch windows snap7 DLL to 64bit version 1.4.2. This also improves UnitTest stability (reduces false positives) on the CI (including appveyor)
- Changing the port used for S7NetTests when communicating with Snap7 to a value > 1000 allows tests to run on Linux without elevated privileges.

S7.Net.UnitTest/Helpers/S7TestServer.cs

@@ -29,7 +29,7 @@ namespace S7.Net.UnitTest.Helpers
             Console.WriteLine(Server.EventText(ref Event));
         }
 
-        public static void Start()
+        public static void Start(short port)
         {
             Server = new S7Server();
             // Share some resources with our virtual PLC
@@ -59,7 +59,14 @@ namespace S7.Net.UnitTest.Helpers
             // Start the server onto the default adapter.
             // To select an adapter we have to use Server->StartTo("192.168.x.y").
             // Start() is the same of StartTo("0.0.0.0");       
+
+            Server.SetParam(S7Consts.p_u16_LocalPort, ref port);
+
             int Error = Server.Start();
+            if (Error != 0)
+            {
+                throw new Exception($"Error starting Snap7 server: {Server.ErrorText(Error)}");
+            }
             //if (Error == 0)
             //{
             //    // Now the server is running ... wait a key to terminate

S7.Net.UnitTest/S7.Net.UnitTest.csproj

@@ -1,15 +1,17 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net452</TargetFrameworks>
+    <TargetFrameworks>net452;netcoreapp3.1</TargetFrameworks>
 
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>Properties\S7.Net.snk</AssemblyOriginatorKeyFile>
     <IsPackable>false</IsPackable>
     <Copyright>Copyright ©  2014</Copyright>
+    <PlatformTarget>x64</PlatformTarget>
   </PropertyGroup>
   
   <ItemGroup>
+    <PackageReference Include="GitHubActionsTestLogger" Version="1.1.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.7.0" />
     <PackageReference Include="MSTest.TestAdapter" Version="2.1.2" />
     <PackageReference Include="MSTest.TestFramework" Version="2.1.2" />
@@ -23,14 +25,13 @@
     <ProjectReference Include="..\S7.Net\S7.Net.csproj" />
   </ItemGroup>
 
-  <ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)'=='net452'">
     <Reference Include="System.ServiceProcess" />
   </ItemGroup>
 
   <ItemGroup>
-    <None Update="snap7.dll">
+    <None Update="runtimes\win-x64\native\snap7.dll" Link="snap7.dll">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </None>
   </ItemGroup>
-
 </Project>

S7.Net.UnitTest/S7NetTestsAsync.cs

@@ -6,10 +6,12 @@ using Microsoft.VisualStudio.TestTools.UnitTesting;
 using S7.Net;
 using S7.Net.UnitTest.Helpers;
 using S7.Net.UnitTest;
-using System.ServiceProcess;
 using S7.Net.Types;
 using S7.UnitTest.Helpers;
 using System.Threading.Tasks;
+#if NETFRAMEWORK
+using System.ServiceProcess;
+#endif
 using System.Threading;
 
 #endregion

S7.Net.UnitTest/S7NetTestsSync.cs

@@ -6,9 +6,11 @@ using Microsoft.VisualStudio.TestTools.UnitTesting;
 using S7.Net;
 using S7.Net.UnitTest.Helpers;
 using S7.Net.UnitTest;
-using System.ServiceProcess;
 using S7.Net.Types;
 using S7.UnitTest.Helpers;
+#if NETFRAMEWORK
+using System.ServiceProcess;
+#endif
 
 #endregion
 
@@ -41,6 +43,7 @@ namespace S7.Net.UnitTest
         #region Constants
         const int DB2 = 2;
         const int DB4 = 4;
+        const short TestServerPort = 31122;
         #endregion
 
         #region Private fields
@@ -53,16 +56,21 @@ namespace S7.Net.UnitTest
         /// </summary>
         public S7NetTests()
         {
-            plc = new Plc(CpuType.S7300, "127.0.0.1", 0, 2);
+            plc = CreatePlc();
             //ConsoleManager.Show();
             ShutDownServiceS7oiehsx64();
 
         }
 
+        private static Plc CreatePlc()
+        {
+            return new Plc(CpuType.S7300, "localhost", TestServerPort, 0, 2);
+        }
+
         [TestInitialize]
         public void Setup()
         {
-            S7TestServer.Start();
+            S7TestServer.Start(TestServerPort);
             plc.Open();
         }
 
@@ -931,9 +939,9 @@ namespace S7.Net.UnitTest
         {
             plc.Close();
             S7TestServer.Stop();
-            S7TestServer.Start();
+            S7TestServer.Start(TestServerPort);
 
-            var reachablePlc = new Plc(CpuType.S7300, "127.0.0.1", 0, 2);
+            var reachablePlc = CreatePlc();
             Assert.IsTrue(reachablePlc.IsAvailable);
         }
 
@@ -1028,6 +1036,7 @@ namespace S7.Net.UnitTest
         #region Private methods
         private static void ShutDownServiceS7oiehsx64()
         {
+#if NETFRAMEWORK
             ServiceController[] services = ServiceController.GetServices();
             var service = services.FirstOrDefault(s => s.ServiceName == "s7oiehsx64");
             if (service != null)
@@ -1037,6 +1046,7 @@ namespace S7.Net.UnitTest
                     service.Stop();
                 }
             }
+#endif
         }
 
         #region IDisposable Support

S7.Net.UnitTest/Snap7/snap7.net.cs

@@ -36,11 +36,8 @@ namespace Snap7
 
     public class S7Consts
     {
-        #if __MonoCS__  // Assuming that we are using Unix release of Mono (otherwise modify it)
-        public const string Snap7LibName = "libsnap7.so";
-        #else
-        public const string Snap7LibName = "snap7.dll";
-        #endif
+        public const string Snap7LibName = "snap7";
+
         //------------------------------------------------------------------------------
         //                                  PARAMS LIST            
         //------------------------------------------------------------------------------