Added RequiresSymbolicLinksTheoryAttribute

src/Tasks.UnitTests/Microsoft.Build.Tasks.UnitTests.csproj

@@ -63,6 +63,7 @@
       <Link>Shared\LongPathSupportDisabledFactAttribute.cs</Link>
     </Compile>
     <Compile Include="..\UnitTests.Shared\RequiresSymbolicLinksFactAttribute.cs" />
+    <Compile Include="..\UnitTests.Shared\RequiresSymbolicLinksTheoryAttribute.cs" />
 
     <EmbeddedResource Include="SampleResx" />
     <EmbeddedResource Include="AssemblyDependency\CacheFileSamples\Microsoft.VisualStudio.LanguageServices.Implementation.csprojAssemblyReference.cache" />

src/UnitTests.Shared/RequiresSymbolicLinksTheoryAttribute.cs

@@ -0,0 +1,55 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.IO;
+
+using Microsoft.Build.Shared;
+using Xunit;
+
+namespace Microsoft.Build.UnitTests
+{
+    /// <summary>
+    /// A custom <see cref="FactAttribute"/> that skips the test if the OS doesn't support creating symlinks.
+    /// </summary>
+    public sealed class RequiresSymbolicLinksTheoryAttribute : TheoryAttribute
+    {
+        private static readonly bool s_runningInAzurePipeline =
+            bool.TryParse(Environment.GetEnvironmentVariable("TF_BUILD"), out bool value) && value;
+
+        public RequiresSymbolicLinksTheoryAttribute()
+        {
+            if (s_runningInAzurePipeline || !NativeMethodsShared.IsWindows)
+            {
+                return;
+            }
+
+            // In Windows, a process can create symlinks only if it has sufficient permissions.
+            // We simply try to create one and if it fails we skip the test.
+            string sourceFile = FileUtilities.GetTemporaryFile();
+            string destinationFile = FileUtilities.GetTemporaryFile();
+            try
+            {
+                File.Create(sourceFile).Dispose();
+
+                string? errorMessage = null;
+                if (!NativeMethodsShared.MakeSymbolicLink(destinationFile, sourceFile, ref errorMessage))
+                {
+                    Skip = "Requires permission to create symbolic links. Need to be run elevated or under development mode " +
+                        "(https://learn.microsoft.com/en-us/windows/apps/get-started/enable-your-device-for-development).";
+                }
+            }
+            finally
+            {
+                if (File.Exists(sourceFile))
+                {
+                    File.Delete(sourceFile);
+                }
+                if (File.Exists(destinationFile))
+                {
+                    File.Delete(destinationFile);
+                }
+            }
+        }
+    }
+}