Tests: handle unavailable Windows symlink privilege

CONTRIBUTING.md

@@ -26,7 +26,11 @@ Use the following shell command:
 ```console
 $ dotnet test
 ```
-Tests involving symlink creation require elevated privileges on Windows, as this is enforced at the OS level.
+
+On Windows, tests that create symbolic links require either [Developer Mode][windows-developer-mode] or an elevated
+process. Developer Mode lets an unelevated process create symbolic links, as documented for the
+[`CreateSymbolicLinkW`][create-symbolic-link] API. When neither is available, these tests are skipped locally; CI
+runners fail instead, ensuring that the tests are not silently skipped in automation.
 
 Test Documentation
 ------------------
@@ -73,6 +77,8 @@ Then run the following shell command:
 $ dotnet fsi scripts/github-actions.fsx
 ```
 
+[create-symbolic-link]: https://learn.microsoft.com/windows/win32/api/winbase/nf-winbase-createsymboliclinkw
 [dotnet-sdk]: https://dotnet.microsoft.com/en-us/download
 [powershell]: https://learn.microsoft.com/en-us/powershell/scripting/install/installing-powershell
 [reuse]: https://reuse.software/
+[windows-developer-mode]: https://learn.microsoft.com/windows/apps/get-started/enable-your-device-for-development

TruePath.Tests/AbsolutePathTests.cs

@@ -135,18 +135,7 @@ public void ReadKind_IsSymlink()
 
         var tempDirectoryInfo = Path.GetTempPath();
 
-        try
-        {
-            Directory.CreateSymbolicLink(currentDirectory, tempDirectoryInfo);
-        }
-        catch (IOException e) when (OperatingSystem.IsWindows() && !Utils.RunsOnCi())
-        {
-            if (e.Message.Contains("privilege") && (e.StackTrace?.Contains("CreateSymbolicLink") ?? false))
-            {
-                Assert.Skip("Tests involving symlink creation require elevated privileges on Windows, as this is enforced at the OS level.");
-            }
-            else throw;
-        }
+        Utils.CreateSymbolicLinkOrSkip(() => Directory.CreateSymbolicLink(currentDirectory, tempDirectoryInfo));
 
         // Act
         var kind = localPath.ReadKind();

TruePath.Tests/Utils.cs

@@ -2,6 +2,8 @@
 //
 // SPDX-License-Identifier: MIT
 
+using Windows.Win32;
+using Windows.Win32.Foundation;
 using Xunit.v3;
 
 namespace TruePath.Tests;
@@ -44,6 +46,24 @@ internal static bool RunsOnCi()
         return Environment.GetEnvironmentVariable("CI") is not null;
     }
 
+    internal static void CreateSymbolicLinkOrSkip(Action createSymbolicLink)
+    {
+        try
+        {
+            createSymbolicLink();
+        }
+        catch (IOException e) when (OperatingSystem.IsWindows()
+                                    && e.HResult == PInvoke.HRESULT_FROM_WIN32(WIN32_ERROR.ERROR_PRIVILEGE_NOT_HELD).Value)
+        {
+            Assert.False(
+                RunsOnCi(),
+                "CI runners must allow symbolic link creation so these tests are not skipped silently.");
+            Assert.Skip(
+                "Creating symbolic links on Windows requires Developer Mode or an elevated process. " +
+                "See CONTRIBUTING.md for setup instructions.");
+        }
+    }
+
     /// <summary>
     /// Changes the current directory to <paramref name="newDirectory"/>, and restores the previous one on disposal.
     /// </summary>

TruePath/NativeMethods.txt

@@ -7,4 +7,6 @@ FILE_ACCESS_RIGHTS
 FILE_ATTRIBUTE_TAG_INFO
 GetFileInformationByHandleEx
 GetFinalPathNameByHandle
+HRESULT_FROM_WIN32
 IO_REPARSE_TAG_MOUNT_POINT
+WIN32_ERROR