Implement simple LSP run tests

eng/Versions.props

@@ -42,7 +42,7 @@
     <SourceGeneratorMicrosoftCodeAnalysisVersion>4.1.0</SourceGeneratorMicrosoftCodeAnalysisVersion>
     <MicrosoftILVerificationVersion>7.0.0-alpha.1.22060.1</MicrosoftILVerificationVersion>
     <MicrosoftVisualStudioThreadingPackagesVersion>17.7.1-preview</MicrosoftVisualStudioThreadingPackagesVersion>
-    <MicrosoftTestPlatformVersion>17.4.0-preview-20220707-01</MicrosoftTestPlatformVersion>
+    <MicrosoftTestPlatformVersion>17.4.1</MicrosoftTestPlatformVersion>
   </PropertyGroup>
   <!--
     Dependency versions

src/Features/CSharp/Portable/Testing/CSharpTestMethodFinder.cs

@@ -0,0 +1,51 @@
+// 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 System;
+using System.Collections.Generic;
+using System.Composition;
+using System.Linq;
+using Microsoft.CodeAnalysis.CSharp.Extensions;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Features.Testing;
+using Microsoft.CodeAnalysis.Host.Mef;
+
+namespace Microsoft.CodeAnalysis.CSharp.Testing;
+
+[ExportLanguageService(typeof(ITestMethodFinder), LanguageNames.CSharp), Shared]
+[method: ImportingConstructor]
+[method: Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
+internal class CSharpTestMethodFinder([ImportMany] IEnumerable<ITestFrameworkMetadata> testFrameworks) : AbstractTestMethodFinder<MethodDeclarationSyntax>(testFrameworks)
+{
+    protected override bool DescendIntoChildren(SyntaxNode node)
+    {
+        // We only need to look in type declarations for test methods (and therefore namespaces to find types).
+        return node is BaseNamespaceDeclarationSyntax or TypeDeclarationSyntax;
+    }
+
+    protected override bool IsTestMethod(MethodDeclarationSyntax method)
+    {
+        foreach (var attributeList in method.AttributeLists)
+        {
+            foreach (var attribute in attributeList.Attributes)
+            {
+                var isTestAttribute = IsTestAttribute(attribute);
+                if (isTestAttribute)
+                {
+                    return true;
+                }
+            }
+        }
+
+        return false;
+    }
+
+    private bool IsTestAttribute(AttributeSyntax attribute)
+    {
+        var attributeName = attribute.Name.GetNameToken().Text;
+
+        var matches = TestFrameworkMetadata.Any(metadata => metadata.MatchesAttributeSyntacticName(attributeName));
+        return matches;
+    }
+}