test: add unit tests for controls and rendering helpers

Add comprehensive test coverage for 20+ Skia controls including ActivityIndicator, Border, CheckBox, CollectionView, DatePicker, Editor, Grid, Image, ImageButton, Label, NavigationPage, Page, Picker, ProgressBar, RadioButton, SearchBar, Stepper, Switch, and TimePicker. Include tests for TextRenderingHelper utility methods covering color conversion, font style mapping, and font family resolution.

tests/Views/SkiaBorderTests.cs

@@ -0,0 +1,98 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using FluentAssertions;
+using Microsoft.Maui.Graphics;
+using Microsoft.Maui.Platform;
+using SkiaSharp;
+using Xunit;
+
+namespace Microsoft.Maui.Controls.Linux.Tests.Views;
+
+public class SkiaBorderTests
+{
+    [Fact]
+    public void Constructor_SetsDefaultValues()
+    {
+        // Arrange & Act
+        var border = new SkiaBorder();
+
+        // Assert
+        border.StrokeThickness.Should().Be(1.0);
+        border.CornerRadius.Should().Be(0.0);
+        border.Stroke.Should().Be(Colors.Black);
+        border.HasShadow.Should().BeFalse();
+        border.IsVisible.Should().BeTrue();
+        border.IsEnabled.Should().BeTrue();
+    }
+
+    [Fact]
+    public void Content_WhenSet_UpdatesProperty()
+    {
+        // Arrange
+        var border = new SkiaBorder();
+        var content = new SkiaLabel();
+
+        // Act
+        border.AddChild(content);
+
+        // Assert
+        border.Children.Should().Contain(content);
+        content.Parent.Should().Be(border);
+    }
+
+    [Fact]
+    public void StrokeColor_WhenSet_UpdatesProperty()
+    {
+        // Arrange
+        var border = new SkiaBorder();
+        var color = Microsoft.Maui.Graphics.Colors.Blue;
+
+        // Act
+        border.Stroke = color;
+
+        // Assert
+        border.Stroke.Should().Be(color);
+    }
+
+    [Fact]
+    public void StrokeThickness_WhenSet_UpdatesProperty()
+    {
+        // Arrange
+        var border = new SkiaBorder();
+
+        // Act
+        border.StrokeThickness = 3.0;
+
+        // Assert
+        border.StrokeThickness.Should().Be(3.0);
+    }
+
+    [Fact]
+    public void CornerRadius_WhenSet_UpdatesProperty()
+    {
+        // Arrange
+        var border = new SkiaBorder();
+
+        // Act
+        border.CornerRadius = 12.0;
+
+        // Assert
+        border.CornerRadius.Should().Be(12.0);
+    }
+
+    [Fact]
+    public void Draw_DoesNotThrow()
+    {
+        // Arrange
+        var border = new SkiaBorder();
+        border.Bounds = new Rect(0, 0, 200, 100);
+
+        using var surface = SKSurface.Create(new SKImageInfo(300, 200));
+        var canvas = surface.Canvas;
+
+        // Act & Assert
+        var exception = Record.Exception(() => border.Draw(canvas));
+        exception.Should().BeNull();
+    }
+}