Added: Tests for the new functionality

src/NexusMods.Paths/Utilities/FileSystemMarshal.cs

@@ -1,10 +1,9 @@
-using System.Diagnostics.CodeAnalysis;
-
 namespace NexusMods.Paths.Utilities;
 
 /// <summary>
-///     This is a suite of low level methods that provide 'escape hatches' for the
-///     file system abstraction where lower level access is required.
+///     This is a suite of low level methods that provide 'escape hatches' and
+///     other utilities for the file system abstraction where lower level access
+///     is required.
 /// </summary>
 /// <remarks>
 ///     This is named after classes like
@@ -31,7 +30,7 @@ public static class FileSystemMarshal
     ///     that works with the <see cref="IFileSystem"/> abstraction, or throw
     ///     an exception.
     /// </remarks>
-    public static bool TryResolveRealFilesystemPath(AbsolutePath path, [MaybeNullWhen(false)] out string? fullFilePath)
+    public static bool TryResolveRealFilesystemPath(AbsolutePath path, out string? fullFilePath)
     {
         // Only paths from the Real 'FileSystem' can be resolved here.
         if (path.FileSystem is not FileSystem realFs)

tests/NexusMods.Paths.Tests/FileSystem/BaseFileSystemTests.cs

@@ -2,6 +2,7 @@
 using System.Runtime.InteropServices;
 using FluentAssertions;
 using NexusMods.Paths.TestingHelpers;
+using NexusMods.Paths.Utilities;
 
 namespace NexusMods.Paths.Tests.FileSystem;
 
@@ -251,4 +252,60 @@ public void Test_KnownPath(string os, KnownPath knownPath, bool expected)
         if (expected) act.Should().NotThrow();
         else act.Should().Throw<Exception>();
     }
+
+    [Fact]
+    public void TryResolveRealFilesystemPath_WithRealFileSystem_ReturnsTrue()
+    {
+        // Arrange
+        var fs = new Paths.FileSystem();
+        using var tempManager = new TemporaryFileManager(fs);
+        using var tempFile = tempManager.CreateFile();
+
+        // Act
+        var result = FileSystemMarshal.TryResolveRealFilesystemPath(tempFile, out var resolvedPath);
+
+        // Assert
+        result.Should().BeTrue();
+        resolvedPath.Should().Be(tempFile.Path.GetFullPath());
+    }
+
+    [Fact]
+    public void TryResolveRealFilesystemPath_WithInMemoryFileSystem_ReturnsFalse()
+    {
+        // Arrange
+        var fs = new InMemoryFileSystem();
+        using var tempManager = new TemporaryFileManager(fs);
+        using var tempFile = tempManager.CreateFile();
+
+        // Act
+        var result = FileSystemMarshal.TryResolveRealFilesystemPath(tempFile, out var resolvedPath);
+
+        // Assert
+        result.Should().BeFalse();
+    }
+
+    [Fact]
+    public void TryResolveRealFilesystemPath_WithMappedPath_ResolvesCorrectly()
+    {
+        // Arrange
+        var fs = new Paths.FileSystem();
+        using var tempManager = new TemporaryFileManager(fs);
+        using var tempFile1 = tempManager.CreateFile();
+        using var tempFile2 = tempManager.CreateFile();
+        var originalPath = tempFile1.Path;
+        var mappedPath = tempFile2.Path;
+
+        var overlayFileSystem = fs.CreateOverlayFileSystem(new Dictionary<AbsolutePath, AbsolutePath>
+        {
+            { originalPath, mappedPath }
+        }, new Dictionary<KnownPath, AbsolutePath>());
+
+        // Act
+        var source = overlayFileSystem.FromUnsanitizedFullPath(originalPath.GetFullPath());
+        var result = FileSystemMarshal.TryResolveRealFilesystemPath(source, out var resolvedPath);
+
+        // Assert
+        result.Should().BeTrue();
+        resolvedPath.Should().Be(mappedPath.GetFullPath());
+    }
 }

tests/NexusMods.Paths.Tests/NexusMods.Paths.Tests.csproj

@@ -14,4 +14,8 @@
             <CopyToOutputDirectory>Always</CopyToOutputDirectory>
         </None>
     </ItemGroup>
+
+    <ItemGroup>
+      <Folder Include="Utilities\" />
+    </ItemGroup>
 </Project>