Fix build.

ICSharpCode.Decompiler.Tests/Helpers/Tester.cs

@@ -219,7 +219,9 @@ namespace ICSharpCode.Decompiler.Tests.Helpers
 
 		static readonly RoslynToolset roslynToolset = new RoslynToolset();
 
-		static readonly string coreRefAsmPath = new DotNetCorePathFinder(TargetFrameworkIdentifier.NETCoreApp, new Version(3, 1)).GetReferenceAssemblyPath(".NETCoreApp, Version = v3.1");
+		static readonly string coreRefAsmPath = new DotNetCorePathFinder(TargetFrameworkIdentifier.NETCoreApp,
+			new Version(3, 1), "Microsoft.NETCore.App")
+				.GetReferenceAssemblyPath(".NETCoreApp, Version = v3.1");
 
 		static readonly string refAsmPath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ProgramFilesX86),
 			@"Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2");
@@ -628,7 +630,7 @@ namespace ICSharpCode.Decompiler.Tests.Helpers
 			{
 				var module = new PEFile(assemblyFileName, file, PEStreamOptions.PrefetchEntireImage);
 				var resolver = new UniversalAssemblyResolver(assemblyFileName, false,
-					module.Reader.DetectTargetFrameworkId(), PEStreamOptions.PrefetchMetadata);
+					module.Reader.DetectTargetFrameworkId(), null, PEStreamOptions.PrefetchMetadata);
 				resolver.AddSearchDirectory(Path.GetDirectoryName(typeof(Span<>).Assembly.Location));
 				var typeSystem = new DecompilerTypeSystem(module, resolver, settings);
 				CSharpDecompiler decompiler = new CSharpDecompiler(typeSystem, settings);

ICSharpCode.Decompiler.Tests/PdbGenerationTestRunner.cs

@@ -59,7 +59,7 @@ namespace ICSharpCode.Decompiler.Tests
 			string peFileName = Path.Combine(TestCasePath, testName + ".expected.dll");
 			string pdbFileName = Path.Combine(TestCasePath, testName + ".expected.pdb");
 			var moduleDefinition = new PEFile(peFileName);
-			var resolver = new UniversalAssemblyResolver(peFileName, false, moduleDefinition.Reader.DetectTargetFrameworkId(), PEStreamOptions.PrefetchEntireImage);
+			var resolver = new UniversalAssemblyResolver(peFileName, false, moduleDefinition.Reader.DetectTargetFrameworkId(), null, PEStreamOptions.PrefetchEntireImage);
 			var decompiler = new CSharpDecompiler(moduleDefinition, resolver, new DecompilerSettings());
 			using (FileStream pdbStream = File.Open(Path.Combine(TestCasePath, testName + ".pdb"), FileMode.OpenOrCreate, FileAccess.ReadWrite))
 			{

ICSharpCode.Decompiler.Tests/TestAssemblyResolver.cs

@@ -13,7 +13,7 @@ namespace ICSharpCode.Decompiler.Tests
 		readonly HashSet<string> localAssemblies = new HashSet<string>();
 
 		public TestAssemblyResolver(string mainAssemblyFileName, string baseDir, string targetFramework)
-			: base(mainAssemblyFileName, false, targetFramework, PEStreamOptions.PrefetchMetadata, MetadataReaderOptions.ApplyWindowsRuntimeProjections)
+			: base(mainAssemblyFileName, false, targetFramework, null, PEStreamOptions.PrefetchMetadata, MetadataReaderOptions.ApplyWindowsRuntimeProjections)
 		{
 			var assemblyNames = new DirectoryInfo(baseDir).EnumerateFiles("*.dll").Select(f => Path.GetFileNameWithoutExtension(f.Name));
 			foreach (var name in assemblyNames)