update

tests/TraceCad.Tests/DxfExporterTests.cs

@@ -33,4 +33,29 @@ public sealed class DxfExporterTests
             }
         }
     }
+
+    [Fact]
+    public void ExportRejectsInvalidDrawing()
+    {
+        var document = SketchDocument.CreateDefault();
+        document.AddEntity(new LineEntity(Guid.NewGuid(), Layer.Cut.Name, new Point2(5, 5), new Point2(5, 5)));
+
+        var path = Path.Combine(Path.GetTempPath(), $"{Guid.NewGuid():N}.dxf");
+
+        try
+        {
+            var exception = Assert.Throws<InvalidOperationException>(() =>
+                new NetDxfExporter().Export(document, path));
+
+            Assert.Contains("Cannot export invalid drawing", exception.Message);
+            Assert.False(File.Exists(path));
+        }
+        finally
+        {
+            if (File.Exists(path))
+            {
+                File.Delete(path);
+            }
+        }
+    }
 }