refactor: organize test project into subdirectories by feature area

Move 43 root-level test files into feature-specific subdirectories
mirroring the main codebase structure: Geometry, Fill, BestFit, CutOffs,
CuttingStrategy, Engine, IO. Update namespaces to match folder paths.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest.Tests/Fill/IterativeShrinkFillerTests.cs

@@ -0,0 +1,147 @@
+using OpenNest.Engine.Fill;
+using OpenNest.Geometry;
+
+namespace OpenNest.Tests.Fill;
+
+public class IterativeShrinkFillerTests
+{
+    [Fact]
+    public void Fill_NullItems_ReturnsEmpty()
+    {
+        Func<NestItem, Box, List<Part>> fillFunc = (ni, b) => new List<Part>();
+        var result = IterativeShrinkFiller.Fill(null, new Box(0, 0, 100, 100), fillFunc, 1.0);
+
+        Assert.Empty(result.Parts);
+        Assert.Empty(result.Leftovers);
+    }
+
+    [Fact]
+    public void Fill_EmptyItems_ReturnsEmpty()
+    {
+        Func<NestItem, Box, List<Part>> fillFunc = (ni, b) => new List<Part>();
+        var result = IterativeShrinkFiller.Fill(new List<NestItem>(), new Box(0, 0, 100, 100), fillFunc, 1.0);
+
+        Assert.Empty(result.Parts);
+        Assert.Empty(result.Leftovers);
+    }
+
+    private static Drawing MakeRectDrawing(double w, double h, string name = "rect")
+    {
+        var pgm = new OpenNest.CNC.Program();
+        pgm.Codes.Add(new OpenNest.CNC.RapidMove(new Vector(0, 0)));
+        pgm.Codes.Add(new OpenNest.CNC.LinearMove(new Vector(w, 0)));
+        pgm.Codes.Add(new OpenNest.CNC.LinearMove(new Vector(w, h)));
+        pgm.Codes.Add(new OpenNest.CNC.LinearMove(new Vector(0, h)));
+        pgm.Codes.Add(new OpenNest.CNC.LinearMove(new Vector(0, 0)));
+        return new Drawing(name, pgm);
+    }
+
+    [Fact]
+    public void Fill_SingleItem_PlacesParts()
+    {
+        var drawing = MakeRectDrawing(20, 10);
+        var items = new List<NestItem>
+        {
+            new NestItem { Drawing = drawing, Quantity = 5 }
+        };
+
+        Func<NestItem, Box, List<Part>> fillFunc = (ni, b) =>
+        {
+            var plate = new Plate(b.Width, b.Length);
+            var engine = new DefaultNestEngine(plate);
+            return engine.Fill(ni, b, null, System.Threading.CancellationToken.None);
+        };
+
+        var result = IterativeShrinkFiller.Fill(items, new Box(0, 0, 120, 60), fillFunc, 1.0);
+
+        Assert.True(result.Parts.Count > 0, "Should place parts");
+    }
+
+    [Fact]
+    public void Fill_MultipleItems_PlacesFromBoth()
+    {
+        var items = new List<NestItem>
+        {
+            new NestItem { Drawing = MakeRectDrawing(20, 10, "large"), Quantity = 5 },
+            new NestItem { Drawing = MakeRectDrawing(8, 5, "small"), Quantity = 5 },
+        };
+
+        Func<NestItem, Box, List<Part>> fillFunc = (ni, b) =>
+        {
+            var plate = new Plate(b.Width, b.Length);
+            var engine = new DefaultNestEngine(plate);
+            return engine.Fill(ni, b, null, System.Threading.CancellationToken.None);
+        };
+
+        var result = IterativeShrinkFiller.Fill(items, new Box(0, 0, 120, 60), fillFunc, 1.0);
+
+        var largeCount = result.Parts.Count(p => p.BaseDrawing.Name == "large");
+        var smallCount = result.Parts.Count(p => p.BaseDrawing.Name == "small");
+
+        Assert.True(largeCount > 0, "Should place large parts");
+        Assert.True(smallCount > 0, "Should place small parts in remaining space");
+    }
+
+    [Fact]
+    public void Fill_UnfilledQuantity_ReturnsLeftovers()
+    {
+        // Huge quantity that can't all fit on a small plate
+        var items = new List<NestItem>
+        {
+            new NestItem { Drawing = MakeRectDrawing(20, 10), Quantity = 1000 },
+        };
+
+        Func<NestItem, Box, List<Part>> fillFunc = (ni, b) =>
+        {
+            var plate = new Plate(b.Width, b.Length);
+            var engine = new DefaultNestEngine(plate);
+            return engine.Fill(ni, b, null, System.Threading.CancellationToken.None);
+        };
+
+        var result = IterativeShrinkFiller.Fill(items, new Box(0, 0, 60, 30), fillFunc, 1.0);
+
+        Assert.True(result.Parts.Count > 0, "Should place some parts");
+        Assert.True(result.Leftovers.Count > 0, "Should have leftovers");
+        Assert.True(result.Leftovers[0].Quantity > 0, "Leftover quantity should be positive");
+    }
+
+    [Fact]
+    public void Fill_UnlimitedQuantity_PlacesParts()
+    {
+        var items = new List<NestItem>
+        {
+            new NestItem { Drawing = MakeRectDrawing(20, 10), Quantity = 0 }
+        };
+
+        Func<NestItem, Box, List<Part>> fillFunc = (ni, b) =>
+        {
+            var plate = new Plate(b.Width, b.Length);
+            var engine = new DefaultNestEngine(plate);
+            return engine.Fill(ni, b, null, System.Threading.CancellationToken.None);
+        };
+
+        var result = IterativeShrinkFiller.Fill(items, new Box(0, 0, 120, 60), fillFunc, 1.0);
+
+        Assert.True(result.Parts.Count > 0, "Unlimited qty items should still be placed");
+        Assert.Empty(result.Leftovers); // unlimited items never produce leftovers
+    }
+
+    [Fact]
+    public void Fill_RespectsCancellation()
+    {
+        var cts = new System.Threading.CancellationTokenSource();
+        cts.Cancel();
+
+        var items = new List<NestItem>
+        {
+            new NestItem { Drawing = MakeRectDrawing(20, 10), Quantity = 10 }
+        };
+
+        Func<NestItem, Box, List<Part>> fillFunc = (ni, b) =>
+            new List<Part> { TestHelpers.MakePartAt(0, 0, 10) };
+
+        var result = IterativeShrinkFiller.Fill(items, new Box(0, 0, 100, 100), fillFunc, 1.0, cts.Token);
+
+        Assert.NotNull(result);
+    }
+}