test(engine): add multi-item, leftover, unlimited qty, and cancellation tests for IterativeShrinkFiller

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

OpenNest.Tests/IterativeShrinkFillerTests.cs

@@ -56,4 +56,92 @@ public class IterativeShrinkFillerTests
 
         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);
+    }
 }