Add cross-platform netstandard2.0 test coverage

Directory.Packages.props

@@ -11,6 +11,7 @@
   <ItemGroup>
     <PackageVersion Include="Microsoft.Extensions.AI" Version="$(MicrosoftExtensionsVersion)" />
     <PackageVersion Include="Microsoft.Extensions.AI.Abstractions" Version="$(MicrosoftExtensionsVersion)" />
+    <PackageVersion Include="Microsoft.Bcl.AsyncInterfaces" Version="$(System10Version)" />
     <PackageVersion Include="Microsoft.Extensions.Caching.Abstractions" Version="$(System10Version)" />
     <PackageVersion Include="Microsoft.Extensions.Caching.Memory" Version="$(System10Version)" />
     <PackageVersion Include="Microsoft.Extensions.Hosting.Abstractions" Version="$(System10Version)" />

ModelContextProtocol.slnx

@@ -77,6 +77,7 @@
     <Project Path="tests/ModelContextProtocol.ConformanceServer/ModelContextProtocol.ConformanceServer.csproj" />
     <Project Path="tests/ModelContextProtocol.TestOAuthServer/ModelContextProtocol.TestOAuthServer.csproj" />
     <Project Path="tests/ModelContextProtocol.Tests/ModelContextProtocol.Tests.csproj" />
+    <Project Path="tests/ModelContextProtocol.Netstandard2_0.Tests/ModelContextProtocol.Netstandard2_0.Tests.csproj" />
     <Project Path="tests/ModelContextProtocol.TestServer/ModelContextProtocol.TestServer.csproj" />
     <Project Path="tests/ModelContextProtocol.TestSseServer/ModelContextProtocol.TestSseServer.csproj" />
     <Project Path="tests/ModelContextProtocol.ExperimentalApiRegressionTest/ModelContextProtocol.ExperimentalApiRegressionTest.csproj" />

tests/ModelContextProtocol.Netstandard2_0.Tests/ModelContextProtocol.Netstandard2_0.Tests.csproj

@@ -0,0 +1,98 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <!--
+    This project provides test coverage for the netstandard2.0 assets of the MCP libraries on a modern
+    .NET runtime (i.e. independent of .NET Framework). It compiles the same test sources as
+    ModelContextProtocol.Tests, but forces the product project references to resolve to their
+    netstandard2.0 build via SetTargetFramework.
+
+    On Windows, the netstandard2.0 assets are also exercised through the net472 target of
+    ModelContextProtocol.Tests (on .NET Framework); this project additionally validates them on a
+    modern .NET runtime on every platform.
+
+    The stdio/external-process integration tests are excluded: they launch a separate net8.0 TestServer
+    process whose (net8.0) product assemblies cannot coexist with the netstandard2.0 product assemblies
+    under test in the same output directory. Those scenarios remain covered by ModelContextProtocol.Tests.
+  -->
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+    <RootNamespace>ModelContextProtocol.Tests</RootNamespace>
+    <!-- https://github.com/dotnet/sdk/issues/51060 -->
+    <NoWarn>$(NoWarn);NU1903;NU1902</NoWarn>
+    <!-- Define for conditional TimeProvider support in InMemoryMcpTaskStore -->
+    <DefineConstants>$(DefineConstants);MCP_TEST_TIME_PROVIDER</DefineConstants>
+  </PropertyGroup>
+
+  <PropertyGroup>
+    <!-- Without this, tests are currently not showing results until all tests complete
+         https://xunit.net/docs/getting-started/v3/microsoft-testing-platform
+    -->
+    <DisableTestingPlatformServerCapability>true</DisableTestingPlatformServerCapability>
+  </PropertyGroup>
+
+  <!-- Compile the same test sources as ModelContextProtocol.Tests, excluding the external-process
+       integration tests (see comment above). -->
+  <ItemGroup>
+    <Compile Include="..\ModelContextProtocol.Tests\**\*.cs"
+             Exclude="..\ModelContextProtocol.Tests\obj\**\*.cs;..\ModelContextProtocol.Tests\bin\**\*.cs;..\ModelContextProtocol.Tests\ClientIntegrationTestFixture.cs;..\ModelContextProtocol.Tests\ClientIntegrationTests.cs;..\ModelContextProtocol.Tests\StdioServerIntegrationTests.cs;..\ModelContextProtocol.Tests\DockerEverythingServerTests.cs;..\ModelContextProtocol.Tests\Transport\StdioClientTransportTests.cs" />
+    <Compile Include="..\Common\**\*.cs" />
+    <!-- Link InMemoryMcpTaskStore.cs for testing with TimeProvider support -->
+    <Compile Include="..\..\src\ModelContextProtocol.Core\Server\InMemoryMcpTaskStore.cs" Link="Server\InMemoryMcpTaskStore.cs" />
+    <!-- Include dependencies for the linked InMemoryMcpTaskStore.cs -->
+    <Compile Include="..\..\src\Common\Experimentals.cs" Link="Experimentals.cs" />
+    <Compile Include="..\..\src\Common\McpHttpHeaders.cs" Link="McpHttpHeaders.cs" />
+    <Compile Include="..\..\src\ModelContextProtocol\Server\DistributedCacheEventIdFormatter.cs" Link="DistributedCacheEventIdFormatter.cs" />
+    <Compile Include="..\..\src\Common\Polyfills\System\IdHelpers.cs" Link="Polyfills\IdHelpers.cs" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+    <!-- The netstandard2.0 product assemblies depend on Microsoft.Bcl.AsyncInterfaces 10.x, but a
+         transitive netstandard2.1 dependency pulls in 6.0.0, which would otherwise win and cause a
+         FileNotFoundException at runtime. Reference it explicitly so the 10.x build is deployed. -->
+    <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" />
+    <PackageReference Include="Microsoft.Extensions.AI" />
+    <PackageReference Include="Microsoft.Extensions.AI.OpenAI" />
+    <PackageReference Include="Microsoft.Extensions.Caching.Memory" />
+    <!-- Provides the Host static class used by tests. In ModelContextProtocol.Tests this comes
+         transitively from the TestServer project references, which aren't used here. -->
+    <PackageReference Include="Microsoft.Extensions.Hosting" />
+    <PackageReference Include="Microsoft.Extensions.Logging" />
+    <PackageReference Include="Microsoft.Extensions.Logging.Console" />
+    <PackageReference Include="Microsoft.Extensions.TimeProvider.Testing" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" />
+    <PackageReference Include="Moq" />
+    <PackageReference Include="OpenTelemetry" />
+    <PackageReference Include="OpenTelemetry.Exporter.InMemory" />
+    <PackageReference Include="Serilog" />
+    <PackageReference Include="JsonSchema.Net" />
+    <PackageReference Include="xunit.v3" />
+    <PackageReference Include="xunit.runner.visualstudio">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+    <!-- net8.0 is not net10.0-compatible, so the polyfill package is required. -->
+    <PackageReference Include="System.Linq.AsyncEnumerable" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <!-- Force the product references to resolve to their netstandard2.0 build. -->
+    <ProjectReference Include="..\..\src\ModelContextProtocol\ModelContextProtocol.csproj">
+      <SetTargetFramework>TargetFramework=netstandard2.0</SetTargetFramework>
+    </ProjectReference>
+    <ProjectReference Include="..\..\src\ModelContextProtocol.Core\ModelContextProtocol.Core.csproj">
+      <SetTargetFramework>TargetFramework=netstandard2.0</SetTargetFramework>
+    </ProjectReference>
+  </ItemGroup>
+
+</Project>