test: add hole subtraction and batch collision tests

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

OpenNest.Tests/CollisionTests.cs

@@ -1,5 +1,6 @@
 using OpenNest.Geometry;
 using OpenNest.Math;
+using System.Collections.Generic;
 
 namespace OpenNest.Tests;
 
@@ -85,6 +86,99 @@ public class CollisionTests
         Assert.True(result.OverlapArea > 0.49 && result.OverlapArea < 0.51);
     }
 
+    /// <summary>
+    /// Square A has a hole. Square B overlaps only the hole area.
+    /// This should NOT be a collision — B fits inside A's cutout.
+    /// </summary>
+    [Fact]
+    public void Check_OverlapInsideHole_ReturnsNone()
+    {
+        var a = MakeSquare(0, 0, 4, 4);
+        var holeA = new List<Polygon> { MakeSquare(1, 1, 3, 3) };
+
+        // B fits entirely inside the hole
+        var b = MakeSquare(1.5, 1.5, 2.5, 2.5);
+
+        var result = Collision.Check(a, b, holesA: holeA);
+
+        Assert.False(result.Overlaps);
+    }
+
+    /// <summary>
+    /// Square A has a hole. Square B partially overlaps the hole and
+    /// partially overlaps solid material. Should still be a collision.
+    /// </summary>
+    [Fact]
+    public void Check_PartialOverlapWithHole_StillOverlaps()
+    {
+        var a = MakeSquare(0, 0, 4, 4);
+        var holeA = new List<Polygon> { MakeSquare(1, 1, 3, 3) };
+
+        // B extends beyond the hole into solid material
+        var b = MakeSquare(2, 2, 5, 5);
+
+        var result = Collision.Check(a, b, holesA: holeA);
+
+        // Hole subtraction uses a conservative approach (keeps partial overlaps),
+        // so we only verify that a collision is still detected for solid material.
+        Assert.True(result.Overlaps);
+    }
+
+    /// <summary>
+    /// HasOverlap with holes returns false when overlap is inside cutout.
+    /// </summary>
+    [Fact]
+    public void HasOverlap_InsideHole_ReturnsFalse()
+    {
+        var a = MakeSquare(0, 0, 4, 4);
+        var holeA = new List<Polygon> { MakeSquare(1, 1, 3, 3) };
+        var b = MakeSquare(1.5, 1.5, 2.5, 2.5);
+
+        Assert.False(Collision.HasOverlap(a, b, holesA: holeA));
+    }
+
+    [Fact]
+    public void CheckAll_MultiplePolygons_FindsAllOverlaps()
+    {
+        var a = MakeSquare(0, 0, 1, 1);
+        var b = MakeSquare(0.5, 0, 1.5, 1);  // overlaps A
+        var c = MakeSquare(5, 5, 6, 6);      // overlaps nobody
+
+        var results = Collision.CheckAll(new List<Polygon> { a, b, c });
+
+        Assert.Single(results);
+        Assert.True(results[0].Overlaps);
+    }
+
+    [Fact]
+    public void CheckAll_NoOverlaps_ReturnsEmpty()
+    {
+        var a = MakeSquare(0, 0, 1, 1);
+        var b = MakeSquare(3, 3, 4, 4);
+
+        var results = Collision.CheckAll(new List<Polygon> { a, b });
+
+        Assert.Empty(results);
+    }
+
+    [Fact]
+    public void HasAnyOverlap_WithOverlap_ReturnsTrue()
+    {
+        var a = MakeSquare(0, 0, 1, 1);
+        var b = MakeSquare(0.5, 0, 1.5, 1);
+
+        Assert.True(Collision.HasAnyOverlap(new List<Polygon> { a, b }));
+    }
+
+    [Fact]
+    public void HasAnyOverlap_NoOverlap_ReturnsFalse()
+    {
+        var a = MakeSquare(0, 0, 1, 1);
+        var b = MakeSquare(3, 3, 4, 4);
+
+        Assert.False(Collision.HasAnyOverlap(new List<Polygon> { a, b }));
+    }
+
     private static Polygon MakeSquare(double left, double bottom, double right, double top)
     {
         var p = new Polygon();