Add failing unit tests demonstrating shadow bug for adornment subviews

Co-authored-by: tig <585482+tig@users.noreply.github.com>

Tests/UnitTestsParallelizable/ViewBase/Adornment/AdornmentSubViewShadowTests.cs

@@ -0,0 +1,242 @@
+using Xunit.Abstractions;
+
+namespace ViewBaseTests.Adornments;
+
+/// <summary>
+/// Tests that demonstrate the bug where shadows of SubViews of Adornments don't draw.
+/// See issue: https://github.com/gui-cs/Terminal.Gui/issues/XXXX
+/// </summary>
+public class AdornmentSubViewShadowTests (ITestOutputHelper output)
+{
+    private readonly ITestOutputHelper _output = output;
+
+    [Fact]
+    public void Button_With_ShadowStyle_In_Padding_Should_Draw_Shadow ()
+    {
+        // Arrange
+        IApplication app = Application.Create ();
+        app.Init ("fake");
+        app.Driver?.SetScreenSize (30, 10);
+
+        Runnable window = new ()
+        {
+            Width = Dim.Fill (),
+            Height = Dim.Fill ()
+        };
+
+        // Setup padding with some thickness so we have space for the button
+        window.Padding!.Thickness = new (3);
+
+        // Add a button with a shadow to the Padding adornment
+        var buttonInPadding = new Button
+        {
+            X = 1,
+            Y = 1,
+            Text = "Button",
+            ShadowStyle = ShadowStyle.Opaque
+        };
+
+        window.Padding.Add (buttonInPadding);
+        app.Begin (window);
+        app.LayoutAndDraw ();
+
+        // Act - Get the screen contents
+        string? actualOutput = app.Driver?.ToString ();
+        _output.WriteLine ("Actual output:");
+        _output.WriteLine (actualOutput ?? "null");
+
+        // Assert - The button shadow should be visible
+        // The shadow should appear as '▖' on the right and '▝▀▀▀▀▀▀▀▀▘' on the bottom
+        // Currently this test will FAIL because the shadow is NOT drawn (demonstrating the bug)
+        
+        // Expected output would show the button with shadow characters (▖, ▝, ▀, ▘)
+        // But currently the shadow is missing
+        Assert.NotNull (actualOutput);
+        Assert.Contains ("▖", actualOutput); // Right shadow character
+        Assert.Contains ("▝", actualOutput); // Bottom-left shadow corner
+        Assert.Contains ("▘", actualOutput); // Bottom-right shadow corner
+    }
+
+    [Fact]
+    public void Button_With_ShadowStyle_In_Margin_Should_Draw_Shadow ()
+    {
+        // Arrange
+        IApplication app = Application.Create ();
+        app.Init ("fake");
+        app.Driver?.SetScreenSize (30, 10);
+
+        Runnable window = new ()
+        {
+            Width = Dim.Fill (),
+            Height = Dim.Fill ()
+        };
+
+        // Setup margin with some thickness
+        window.Margin!.Thickness = new (3);
+        // Turn off transparent flags for easier testing
+        window.Margin.ViewportSettings = ViewportSettingsFlags.None;
+
+        // Add a button with a shadow to the Margin adornment
+        var buttonInMargin = new Button
+        {
+            X = 1,
+            Y = 1,
+            Text = "Button",
+            ShadowStyle = ShadowStyle.Opaque
+        };
+
+        window.Margin.Add (buttonInMargin);
+        app.Begin (window);
+        app.LayoutAndDraw ();
+
+        // Act - Get the screen contents
+        string? actualOutput = app.Driver?.ToString ();
+        _output.WriteLine ("Actual output:");
+        _output.WriteLine (actualOutput ?? "null");
+
+        // Assert - The button shadow should be visible
+        // Currently this test will FAIL because the shadow is NOT drawn (demonstrating the bug)
+        Assert.NotNull (actualOutput);
+        Assert.Contains ("▖", actualOutput); // Right shadow character
+        Assert.Contains ("▝", actualOutput); // Bottom-left shadow corner
+        Assert.Contains ("▘", actualOutput); // Bottom-right shadow corner
+    }
+
+    [Fact]
+    public void Button_With_ShadowStyle_In_Border_Should_Draw_Shadow ()
+    {
+        // Arrange
+        IApplication app = Application.Create ();
+        app.Init ("fake");
+        app.Driver?.SetScreenSize (30, 10);
+
+        Runnable window = new ()
+        {
+            Width = Dim.Fill (),
+            Height = Dim.Fill ()
+        };
+
+        // Setup border with some thickness
+        window.Border!.Thickness = new (3);
+
+        // Add a button with a shadow to the Border adornment
+        var buttonInBorder = new Button
+        {
+            X = 1,
+            Y = 1,
+            Text = "Button",
+            ShadowStyle = ShadowStyle.Opaque
+        };
+
+        window.Border.Add (buttonInBorder);
+        app.Begin (window);
+        app.LayoutAndDraw ();
+
+        // Act - Get the screen contents
+        string? actualOutput = app.Driver?.ToString ();
+        _output.WriteLine ("Actual output:");
+        _output.WriteLine (actualOutput ?? "null");
+
+        // Assert - The button shadow should be visible
+        // Currently this test will FAIL because the shadow is NOT drawn (demonstrating the bug)
+        Assert.NotNull (actualOutput);
+        Assert.Contains ("▖", actualOutput); // Right shadow character
+        Assert.Contains ("▝", actualOutput); // Bottom-left shadow corner
+        Assert.Contains ("▘", actualOutput); // Bottom-right shadow corner
+    }
+
+    [Fact]
+    public void Button_With_Transparent_ShadowStyle_In_Padding_Should_Draw_Shadow ()
+    {
+        // Arrange
+        IApplication app = Application.Create ();
+        app.Init ("fake");
+        app.Driver?.SetScreenSize (30, 10);
+
+        Runnable window = new ()
+        {
+            Width = Dim.Fill (),
+            Height = Dim.Fill (),
+            Text = "XXXXXXXXXXXXXXXXXXXXXXXXXX"
+        };
+
+        // Setup padding with some thickness so we have space for the button
+        window.Padding!.Thickness = new (3);
+
+        // Add a button with a transparent shadow to the Padding adornment
+        var buttonInPadding = new Button
+        {
+            X = 1,
+            Y = 1,
+            Text = "Button",
+            ShadowStyle = ShadowStyle.Transparent
+        };
+        buttonInPadding.Margin!.ShadowSize = new (1, 1);
+
+        window.Padding.Add (buttonInPadding);
+        app.Begin (window);
+        app.LayoutAndDraw ();
+
+        // Act - Get the screen contents
+        string? actualOutput = app.Driver?.ToString ();
+        _output.WriteLine ("Actual output:");
+        _output.WriteLine (actualOutput ?? "null");
+
+        // Assert - For transparent shadow, we expect to see the underlying text ('X') 
+        // rendered with dimmed colors in the shadow area
+        // Currently this test will FAIL because the shadow is NOT drawn (demonstrating the bug)
+        
+        // We need to verify that the shadow area exists by checking that the button's
+        // margin has the expected thickness (which includes the shadow)
+        Assert.NotNull (actualOutput);
+        Assert.Equal (new (0, 0, 1, 1), buttonInPadding.Margin!.Thickness);
+        
+        // The actual visual rendering of the transparent shadow would show dimmed text
+        // but we can't easily verify colors in this test, so we just verify the structure exists
+    }
+
+    [Fact]
+    public void Nested_View_With_ShadowStyle_In_Padding_Should_Draw_Shadow ()
+    {
+        // Arrange
+        IApplication app = Application.Create ();
+        app.Init ("fake");
+        app.Driver?.SetScreenSize (40, 15);
+
+        Runnable window = new ()
+        {
+            Width = Dim.Fill (),
+            Height = Dim.Fill ()
+        };
+
+        // Setup padding with some thickness
+        window.Padding!.Thickness = new (5);
+
+        // Add a view with a shadow to the Padding adornment
+        var viewInPadding = new View
+        {
+            X = 2,
+            Y = 2,
+            Width = 20,
+            Height = 5,
+            ShadowStyle = ShadowStyle.Opaque,
+            BorderStyle = LineStyle.Single
+        };
+
+        window.Padding.Add (viewInPadding);
+        app.Begin (window);
+        app.LayoutAndDraw ();
+
+        // Act - Get the screen contents
+        string? actualOutput = app.Driver?.ToString ();
+        _output.WriteLine ("Actual output:");
+        _output.WriteLine (actualOutput ?? "null");
+
+        // Assert - The view shadow should be visible
+        // Currently this test will FAIL because the shadow is NOT drawn (demonstrating the bug)
+        Assert.NotNull (actualOutput);
+        Assert.Contains ("▖", actualOutput); // Right shadow character
+        Assert.Contains ("▝", actualOutput); // Bottom-left shadow corner
+        Assert.Contains ("▘", actualOutput); // Bottom-right shadow corner
+    }
+}