refactor: convert OpenNest.Test to xUnit project with TestData helper

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

OpenNest.Test/OpenNest.Test.csproj

@@ -0,0 +1,23 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0-windows</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.*" />
+    <PackageReference Include="xunit" Version="2.*" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.*" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\OpenNest.Core\OpenNest.Core.csproj" />
+    <ProjectReference Include="..\OpenNest.Engine\OpenNest.Engine.csproj" />
+    <ProjectReference Include="..\OpenNest.IO\OpenNest.IO.csproj" />
+  </ItemGroup>
+
+</Project>

OpenNest.Test/TestData.cs

@@ -0,0 +1,72 @@
+using OpenNest.IO;
+
+namespace OpenNest.Test;
+
+public static class TestData
+{
+    private static readonly string? BasePath = ResolveBasePath();
+
+    public static bool IsAvailable => BasePath != null;
+
+    public static string SkipReason =>
+        "Test data not found. Set OPENNEST_TEST_DATA env var or clone " +
+        "https://git.thecozycat.net/aj/OpenNest.Test.git to ../OpenNest.Test.Data/";
+
+    public static string GetPath(string filename)
+    {
+        if (BasePath == null)
+            throw new InvalidOperationException(SkipReason);
+
+        var path = Path.Combine(BasePath, filename);
+
+        if (!File.Exists(path))
+            throw new FileNotFoundException($"Test fixture not found: {path}");
+
+        return path;
+    }
+
+    public static Nest LoadNest(string filename)
+    {
+        var reader = new NestReader(GetPath(filename));
+        return reader.Read();
+    }
+
+    public static Plate CleanPlateFrom(Plate reference)
+    {
+        var plate = new Plate();
+        plate.Size = reference.Size;
+        plate.PartSpacing = reference.PartSpacing;
+        plate.EdgeSpacing = reference.EdgeSpacing;
+        plate.Quadrant = reference.Quadrant;
+        return plate;
+    }
+
+    private static string? ResolveBasePath()
+    {
+        // 1. Environment variable
+        var envPath = Environment.GetEnvironmentVariable("OPENNEST_TEST_DATA");
+
+        if (!string.IsNullOrEmpty(envPath) && Directory.Exists(envPath))
+            return envPath;
+
+        // 2. Sibling directory (../OpenNest.Test.Data/ relative to solution root)
+        var dir = AppContext.BaseDirectory;
+
+        // Walk up from bin/Debug/net8.0-windows to find the solution root.
+        for (var i = 0; i < 6; i++)
+        {
+            var parent = Directory.GetParent(dir);
+
+            if (parent == null)
+                break;
+
+            dir = parent.FullName;
+            var candidate = Path.Combine(dir, "OpenNest.Test.Data");
+
+            if (Directory.Exists(candidate))
+                return candidate;
+        }
+
+        return null;
+    }
+}