diff --git a/OpenNest.Desktop.Tests/PostProcessorLoaderTests.cs b/OpenNest.Desktop.Tests/PostProcessorLoaderTests.cs
new file mode 100644
index 00000000..6fdf9014
--- /dev/null
+++ b/OpenNest.Desktop.Tests/PostProcessorLoaderTests.cs
@@ -0,0 +1,78 @@
+namespace OpenNest.Desktop.Tests;
+
+/// <summary>
+/// Post processors load from a Posts directory one DLL at a time: a DLL that fails is
+/// reported and the others still load, and the materials they provide are registered.
+/// </summary>
+public sealed class PostProcessorLoaderTests : IDisposable
+{
+    private readonly string directory = Path.Combine(Path.GetTempPath(), "OpenNestDesktopTests", Guid.NewGuid().ToString("N"));
+
+    public PostProcessorLoaderTests() => Directory.CreateDirectory(directory);
+
+    public void Dispose()
+    {
+        try { Directory.Delete(directory, recursive: true); } catch (Exception ex) when (ex is IOException or UnauthorizedAccessException) { }
+    }
+
+    [Fact]
+    public void Load_IsolatesAFailingDllReportsItAndRegistersTheOthersMaterials()
+    {
+        // This test assembly is a post plug-in (it holds MaterialPost); the broken DLL is not .NET at all.
+        File.Copy(typeof(MaterialPost).Assembly.Location, Path.Combine(directory, "Good.Posts.dll"));
+        File.WriteAllText(Path.Combine(directory, "Broken.Posts.dll"), "not an assembly");
+        File.WriteAllText(Path.Combine(directory, "Readme.txt"), "ignored");
+
+        var result = PostProcessorLoader.Load(directory);
+
+        var failure = Assert.Single(result.Failures);
+        Assert.StartsWith("Broken.Posts.dll: ", failure);
+        Assert.Contains(result.PostProcessors, post => post.Name == MaterialPost.PostName);
+        Assert.Contains("Unobtainium", PostProcessorMaterials.Names, StringComparer.Ordinal);
+        Assert.Contains("aluminum 5052", PostProcessorMaterials.Names, StringComparer.Ordinal);
+    }
+
+    [Fact]
+    public void Load_WithoutAPostsDirectory_LoadsNothing()
+    {
+        var result = PostProcessorLoader.Load(Path.Combine(directory, "missing"));
+
+        Assert.Empty(result.PostProcessors);
+        Assert.Empty(result.Failures);
+    }
+
+    [Fact]
+    public void Materials_AreAddedOnceIgnoringCaseAndBlanksInNameOrder()
+    {
+        PostProcessorMaterials.AddFrom(new MaterialPost(["zz Order B", "ZZ ORDER a", " ", "zz order b"]));
+
+        var names = PostProcessorMaterials.Names.Where(n => n.StartsWith("zz", StringComparison.OrdinalIgnoreCase)).ToList();
+        Assert.Equal(["ZZ ORDER a", "zz Order B"], names);
+        Assert.DoesNotContain(" ", PostProcessorMaterials.Names);
+    }
+
+    internal sealed class MaterialPost : IPostProcessor, IMaterialProvidingPostProcessor
+    {
+        public const string PostName = "Material Test Post";
+
+        private readonly IReadOnlyList<string> materials;
+
+        public MaterialPost() : this(["Unobtainium", "aluminum 5052"])
+        {
+        }
+
+        public MaterialPost(IReadOnlyList<string> materials) => this.materials = materials;
+
+        public string Name => PostName;
+
+        public string Author => "Tests";
+
+        public string Description => "Provides materials.";
+
+        public IEnumerable<string> GetMaterialNames() => materials;
+
+        public void Post(Nest nest, Stream outputStream) { }
+
+        public void Post(Nest nest, string outputFile) { }
+    }
+}
diff --git a/OpenNest/PostProcessorLoader.cs b/OpenNest.Desktop/PostProcessorLoader.cs
similarity index 100%
rename from OpenNest/PostProcessorLoader.cs
rename to OpenNest.Desktop/PostProcessorLoader.cs
diff --git a/OpenNest/PostProcessorMaterials.cs b/OpenNest.Desktop/PostProcessorMaterials.cs
similarity index 100%
rename from OpenNest/PostProcessorMaterials.cs
rename to OpenNest.Desktop/PostProcessorMaterials.cs