Add unit test to copy/paste that pass with the PR gui-cs/Terminal.Gui…

…#2835.

tests/BorderColorTests.cs

@@ -1,5 +1,9 @@
 using NUnit.Framework;
+using System.Linq;
+using System.Reflection;
 using Terminal.Gui;
+using TerminalGuiDesigner;
+using TerminalGuiDesigner.Operations;
 
 namespace UnitTests
 {
@@ -11,15 +15,78 @@ public void TestRoundTrip_BorderColors_NeverSet()
             var result = RoundTrip<Window, FrameView>((d, v) =>
             {
                 // Our view should not have any border color to start with
-                Assert.AreEqual(-1,(int) v.Border.BorderBrush);
-                Assert.AreEqual(-1,(int) v.Border.Background);
+                Assert.AreEqual(-1, (int)v.Border.BorderBrush);
+                Assert.AreEqual(-1, (int)v.Border.Background);
 
-            },out _);
+            }, out _);
 
             // Since there were no changes we would expect them to stay the same
             // after reload
             Assert.AreEqual(-1, (int)result.Border.BorderBrush);
             Assert.AreEqual(-1, (int)result.Border.Background);
         }
+
+        [TestCase(true)]
+        [TestCase(false)]
+        public void TestCopyPasteContainer(bool alsoSelectSubElements)
+        {
+            RoundTrip<Window, FrameView>((d, v) =>
+                {
+                    new AddViewOperation(new Label(), d, "lbl1").Do();
+                    new AddViewOperation(new Label(), d, "lbl2").Do();
+
+                    Assert.AreEqual(2, v.GetActualSubviews().Count(), "Expected the FrameView to have 2 children (lbl1 and lbl2)");
+
+                    Design[] toCopy;
+
+                    if (alsoSelectSubElements)
+                    {
+                        var lbl1Design = (Design)d.View.GetActualSubviews().First().Data;
+                        Assert.AreEqual("lbl1", lbl1Design.FieldName);
+
+                        toCopy = new Design[] { d, lbl1Design };
+                    }
+                    else
+                    {
+                        toCopy = new[] { d };
+                    }
+
+                    // copy the FrameView
+                    Assert.IsTrue(new CopyOperation(toCopy).Do());
+
+                    var rootDesign = d.GetRootDesign();
+
+                    // paste the FrameView
+                    Assert.IsTrue(new PasteOperation(rootDesign).Do());
+
+                    var rootSubviews = rootDesign.View.GetActualSubviews();
+
+                    Assert.AreEqual(2, rootSubviews.Count, "Expected root to have 2 FrameView now");
+                    Assert.IsTrue(rootSubviews.All(v => v is FrameView));
+
+                    Assert.IsTrue(
+                        rootSubviews.All(f => f.GetActualSubviews().Count() == 2),
+                        "Expected both FrameView (copied and pasted) to have the full contents of 2 Labels");
+
+                    // Since there were no changes we would expect them to stay the same
+                    // after reload
+                    foreach (var rsv in rootSubviews)
+                    {
+                        Assert.AreEqual(-1, (int)rsv.Border.BorderBrush);
+                        Assert.AreEqual(-1, (int)rsv.Border.Background);
+                        Assert.Null(GetFieldValue<Color?>(rsv.Border, "borderBrush"));
+                        Assert.Null(GetFieldValue<Color?>(rsv.Border, "background"));
+                    }
+                }
+                , out _);
+        }
+
+        private T GetFieldValue<T>(object obj, string name)
+        {
+            // Set the flags so that private and public fields from instances will be found
+            var bindingFlags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance;
+            var field = obj.GetType().GetField(name, bindingFlags);
+            return (T)field?.GetValue(obj)!;
+        }
     }
 }