Switching tests to compile as netstandard2.0 assembly

Author: distantcam

src/Directory.Packages.props

@@ -10,12 +10,11 @@
     <PackageVersion Include="Microsoft.CodeAnalysis.CSharp.SourceGenerators.Testing" Version="1.1.3" />
     <PackageVersion Include="Microsoft.CodeAnalysis.CSharp.Workspaces" Version="4.14.0" />
     <PackageVersion Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="9.0.10" />
-    <PackageVersion Include="Microsoft.NETCore.App.Ref" Version="9.0.10" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.0.1" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.3.0" />
     <PackageVersion Include="Microsoft.SourceLink.GitHub" Version="10.0.103" />
     <PackageVersion Include="TUnit" Version="1.18.21" />
     <PackageVersion Include="Verify.DiffPlex" Version="3.1.2" />
     <PackageVersion Include="Verify.SourceGenerators" Version="2.5.0" />
     <PackageVersion Include="Verify.TUnit" Version="31.13.2" />
   </ItemGroup>
-</Project>
+</Project>

src/Shared/Helpers/CodeBuilder.Templates.cs

@@ -39,7 +39,7 @@ private void AddDebuggerNonUserCodeAttribute()
         => AppendLine("[global::System.Diagnostics.DebuggerNonUserCode]");
 
     // Class | Struct | Constructor | Method | Property | Event
-    private void AddExcludeFromCodeCoverage(string justification = "Generated code.")
+    private void AddExcludeFromCodeCoverage()
         => AppendLine($"[global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]");
 
     public CodeBuilder AddGeneratedAttributes(AttributeTargets attributeTargets)

src/Tests/Utilities/CompilationBuilder.cs

@@ -86,17 +86,27 @@ public CompilationBuilder AddCodes(params IEnumerable<string> codes)
         };
     }
 
-    public async Task<CompilationBuilder> AddNugetReference(string id, string path = "lib", CancellationToken cancellationToken = default)
+    public Task<CompilationBuilder> AddNugetReference(string id, string path = "lib", CancellationToken cancellationToken = default)
     {
         var versionXml = s_packageVersionDoc.Root?.Descendants("PackageVersion")
             .FirstOrDefault(el => el.Attribute("Include")?.Value == id);
         var version = versionXml?.Attribute("Version")?.Value
             ?? throw new InvalidOperationException($"{id} missing from Directory.Packages.props");
+        return AddNugetReference(id, version, path, cancellationToken);
+    }
+
+    public Task<CompilationBuilder> AddNugetReference(string id, string version, string path = "lib", CancellationToken cancellationToken = default)
+    {
         var nugetReference = new ReferenceAssemblies(
             _targetFramework,
             new(id, version),
             Path.Combine(path, _targetFramework));
-        var references = await nugetReference.ResolveAsync(_parseOptions.Language, cancellationToken)
+        return AddReference(nugetReference, cancellationToken);
+    }
+
+    public async Task<CompilationBuilder> AddReference(ReferenceAssemblies reference, CancellationToken cancellationToken = default)
+    {
+        var references = await reference.ResolveAsync(_parseOptions.Language, cancellationToken)
             .ConfigureAwait(false);
         return new(this)
         {

src/Tests/Utilities/ExampleTestsHelper.cs

@@ -1,6 +1,7 @@
 using System.Collections.Immutable;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.Testing;
 using TUnit.Core.Interfaces;
 
 internal static class ExampleTestsHelper
@@ -53,13 +54,31 @@ public virtual async Task InitializeAsync()
                 .WithNullableContextOptions(NullableContextOptions.Enable)
                 .WithPreprocessorSymbols(PreprocessorSymbols);
 
-            Builder = await Builder.AddNugetReference("Microsoft.NETCore.App.Ref", "ref")
+            Builder = await Builder
+                .AddReference(ReferenceAssemblies.NetStandard.NetStandard20)
                 .ConfigureAwait(false);
             foreach (var id in GetNuGetIds())
             {
                 Builder = await Builder.AddNugetReference(id)
                     .ConfigureAwait(false);
             }
+            Builder = Builder.AddCodes(@"
+namespace System.Runtime.CompilerServices;
+
+internal static class IsExternalInit;
+
+[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = false, Inherited = false)]
+internal sealed class RequiredMemberAttribute : Attribute;
+
+[AttributeUsage(AttributeTargets.All, AllowMultiple = true, Inherited = false)]
+public sealed class CompilerFeatureRequiredAttribute(string featureName) : Attribute
+{
+    public string FeatureName { get; } = featureName;
+    public bool IsOptional { get; init; }
+    public const string RefStructs = nameof(RefStructs);
+    public const string RequiredMembers = nameof(RequiredMembers);
+}
+");
         }
 
         protected virtual IEnumerable<string> GetNuGetIds() => [];