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/FillExtentsTests.cs

@@ -0,0 +1,162 @@
+using OpenNest.CNC;
+using OpenNest.Engine.Fill;
+using OpenNest.Geometry;
+
+namespace OpenNest.Tests.Fill;
+
+public class FillExtentsTests
+{
+    private static Drawing MakeRightTriangle(double w, double h)
+    {
+        var pgm = new Program();
+        pgm.Codes.Add(new RapidMove(new Vector(0, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(w, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, h)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, 0)));
+        return new Drawing("triangle", pgm);
+    }
+
+    private static Drawing MakeRect(double w, double h)
+    {
+        var pgm = new Program();
+        pgm.Codes.Add(new RapidMove(new Vector(0, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(w, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(w, h)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, h)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, 0)));
+        return new Drawing("rect", pgm);
+    }
+
+    [Fact]
+    public void Fill_Triangle_ReturnsPartsWithinWorkArea()
+    {
+        var workArea = new Box(0, 0, 120, 60);
+        var filler = new FillExtents(workArea, 0.5);
+        var drawing = MakeRightTriangle(10, 8);
+
+        var parts = filler.Fill(drawing);
+
+        Assert.NotNull(parts);
+        Assert.True(parts.Count > 0, "Should place at least one part");
+
+        foreach (var part in parts)
+        {
+            Assert.True(part.BoundingBox.Right <= workArea.Right + 0.01,
+                $"Part right edge {part.BoundingBox.Right} exceeds work area {workArea.Right}");
+            Assert.True(part.BoundingBox.Top <= workArea.Top + 0.01,
+                $"Part top edge {part.BoundingBox.Top} exceeds work area {workArea.Top}");
+        }
+    }
+
+    [Fact]
+    public void Fill_PartTooLarge_ReturnsEmpty()
+    {
+        var workArea = new Box(0, 0, 5, 5);
+        var filler = new FillExtents(workArea, 0.5);
+        var drawing = MakeRect(10, 10);
+
+        var parts = filler.Fill(drawing);
+
+        Assert.NotNull(parts);
+        Assert.Empty(parts);
+    }
+
+    [Fact]
+    public void Fill_Triangle_ColumnFillsHeight()
+    {
+        var workArea = new Box(0, 0, 120, 60);
+        var filler = new FillExtents(workArea, 0.5);
+        var drawing = MakeRightTriangle(10, 8);
+
+        var parts = filler.Fill(drawing);
+
+        Assert.True(parts.Count > 0);
+
+        // The topmost part should be close to the work area top edge.
+        var topEdge = 0.0;
+        foreach (var part in parts)
+        {
+            if (part.BoundingBox.Top > topEdge)
+                topEdge = part.BoundingBox.Top;
+        }
+
+        // After adjustment, the gap should be small (within one part spacing).
+        var gap = workArea.Top - topEdge;
+        Assert.True(gap < 1.0,
+            $"Gap of {gap:F2} is too large — adjustment should fill close to the top");
+    }
+
+    [Fact]
+    public void Fill_Triangle_FillsWidthWithMultipleColumns()
+    {
+        var workArea = new Box(0, 0, 120, 60);
+        var filler = new FillExtents(workArea, 0.5);
+        var drawing = MakeRightTriangle(10, 8);
+
+        var parts = filler.Fill(drawing);
+
+        // With a 120-wide sheet and ~10-wide parts, we should get multiple columns.
+        Assert.True(parts.Count >= 8,
+            $"Expected multiple columns but got only {parts.Count} parts");
+
+        // Verify all parts are within bounds.
+        foreach (var part in parts)
+        {
+            Assert.True(part.BoundingBox.Right <= workArea.Right + 0.01);
+            Assert.True(part.BoundingBox.Top <= workArea.Top + 0.01);
+            Assert.True(part.BoundingBox.Left >= workArea.Left - 0.01);
+            Assert.True(part.BoundingBox.Bottom >= workArea.Bottom - 0.01);
+        }
+    }
+
+    [Fact]
+    public void Fill_Rect_ReturnsNonEmpty()
+    {
+        var workArea = new Box(0, 0, 120, 60);
+        var filler = new FillExtents(workArea, 0.5);
+        var drawing = MakeRect(15, 10);
+
+        var parts = filler.Fill(drawing);
+
+        Assert.NotNull(parts);
+        Assert.True(parts.Count > 0, "Rectangle should produce results");
+    }
+
+    [Fact]
+    public void Fill_NonZeroOriginWorkArea_PartsWithinBounds()
+    {
+        // Simulate a remnant sub-region with non-zero origin.
+        var workArea = new Box(30, 10, 80, 40);
+        var filler = new FillExtents(workArea, 0.5);
+        var drawing = MakeRightTriangle(10, 8);
+
+        var parts = filler.Fill(drawing);
+
+        Assert.True(parts.Count > 0);
+
+        foreach (var part in parts)
+        {
+            Assert.True(part.BoundingBox.Left >= workArea.Left - 0.01,
+                $"Part left {part.BoundingBox.Left} below work area left {workArea.Left}");
+            Assert.True(part.BoundingBox.Bottom >= workArea.Bottom - 0.01,
+                $"Part bottom {part.BoundingBox.Bottom} below work area bottom {workArea.Bottom}");
+            Assert.True(part.BoundingBox.Right <= workArea.Right + 0.01);
+            Assert.True(part.BoundingBox.Top <= workArea.Top + 0.01);
+        }
+    }
+
+    [Fact]
+    public void Fill_RespectsCancellation()
+    {
+        var cts = new System.Threading.CancellationTokenSource();
+        cts.Cancel();
+
+        var workArea = new Box(0, 0, 120, 60);
+        var filler = new FillExtents(workArea, 0.5);
+        var drawing = MakeRightTriangle(10, 8);
+
+        var parts = filler.Fill(drawing, token: cts.Token);
+
+        Assert.NotNull(parts);
+    }
+}