Added .NET Standard 2.0 test project

Author: Sergio0694

UnitTests/UnitTests.NetStandard/SampleModelWithINPCAndObservableProperties.cs

@@ -0,0 +1,22 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Microsoft.Toolkit.Mvvm.ComponentModel;
+
+namespace UnitTests.NetStandard
+{
+    /// <summary>
+    /// See https://github.com/CommunityToolkit/WindowsCommunityToolkit/issues/3665.
+    /// This model in particular is loaded from an external .NET Standard 2.0 assembly.
+    /// </summary>
+    [INotifyPropertyChanged]
+    public partial class SampleModelWithINPCAndObservableProperties
+    {
+        [ObservableProperty]
+        private int x;
+
+        [ObservableProperty]
+        private int y;
+    }
+}

UnitTests/UnitTests.NetStandard/UnitTests.NetStandard.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+    <LangVersion>9.0</LangVersion>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\Microsoft.Toolkit.Mvvm\Microsoft.Toolkit.Mvvm.csproj" />
+    <ProjectReference Include="..\..\Microsoft.Toolkit.Mvvm.SourceGenerators\Microsoft.Toolkit.Mvvm.SourceGenerators.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" PrivateAssets="contentfiles;build" />
+  </ItemGroup>
+
+</Project>

Windows Community Toolkit (NET).slnf

@@ -10,6 +10,7 @@
       "UnitTests\\UnitTests.HighPerformance.NetCore\\UnitTests.HighPerformance.NetCore.csproj",
       "UnitTests\\UnitTests.HighPerformance.Shared\\UnitTests.HighPerformance.Shared.shproj",
       "UnitTests\\UnitTests.NetCore\\UnitTests.NetCore.csproj",
+      "UnitTests\\UnitTests.NetStandard\\UnitTests.NetStandard.csproj",
       "UnitTests\\UnitTests.Shared\\UnitTests.Shared.shproj",
       "UnitTests\\UnitTests.SourceGenerators\\UnitTests.SourceGenerators.csproj",
     ]

Windows Community Toolkit.sln

@@ -159,7 +159,9 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Toolkit.Uwp.UI.Co
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Toolkit.Mvvm.SourceGenerators", "Microsoft.Toolkit.Mvvm.SourceGenerators\Microsoft.Toolkit.Mvvm.SourceGenerators.csproj", "{E24D1146-5AD8-498F-A518-4890D8BF4937}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "UnitTests.SourceGenerators", "UnitTests\UnitTests.SourceGenerators\UnitTests.SourceGenerators.csproj", "{338C3BE4-2E71-4F21-AD30-03FDBB47A272}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "UnitTests.SourceGenerators", "UnitTests\UnitTests.SourceGenerators\UnitTests.SourceGenerators.csproj", "{338C3BE4-2E71-4F21-AD30-03FDBB47A272}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "UnitTests.NetStandard", "UnitTests\UnitTests.NetStandard\UnitTests.NetStandard.csproj", "{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}"
 EndProject
 Global
 	GlobalSection(SharedMSBuildProjectFiles) = preSolution
@@ -1154,6 +1156,26 @@ Global
 		{338C3BE4-2E71-4F21-AD30-03FDBB47A272}.Release|x64.Build.0 = Release|Any CPU
 		{338C3BE4-2E71-4F21-AD30-03FDBB47A272}.Release|x86.ActiveCfg = Release|Any CPU
 		{338C3BE4-2E71-4F21-AD30-03FDBB47A272}.Release|x86.Build.0 = Release|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Debug|ARM.ActiveCfg = Debug|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Debug|ARM.Build.0 = Debug|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Debug|ARM64.ActiveCfg = Debug|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Debug|ARM64.Build.0 = Debug|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Debug|x64.Build.0 = Debug|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Debug|x86.Build.0 = Debug|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Release|Any CPU.Build.0 = Release|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Release|ARM.ActiveCfg = Release|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Release|ARM.Build.0 = Release|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Release|ARM64.ActiveCfg = Release|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Release|ARM64.Build.0 = Release|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Release|x64.ActiveCfg = Release|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Release|x64.Build.0 = Release|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Release|x86.ActiveCfg = Release|Any CPU
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -1204,6 +1226,7 @@ Global
 		{3307BC1D-5D71-41C6-A1B3-B113B8242D08} = {F1AFFFA7-28FE-4770-BA48-10D76F3E59BC}
 		{099B60FD-DAD6-4648-9DE2-8DBF9DCD9557} = {F1AFFFA7-28FE-4770-BA48-10D76F3E59BC}
 		{338C3BE4-2E71-4F21-AD30-03FDBB47A272} = {B30036C4-D514-4E5B-A323-587A061772CE}
+		{D9C82C0D-31D7-4888-B024-3CF3A4F54FE1} = {B30036C4-D514-4E5B-A323-587A061772CE}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {5403B0C4-F244-4F73-A35C-FE664D0F4345}