Add test cases for ConsoleDriverFactory and IConsoleDriver extensibility

Co-authored-by: shibayan <1356444+shibayan@users.noreply.github.com>

Author: Copilot

Sharprompt.Tests/ConsoleDriverFactoryTests.cs

@@ -0,0 +1,103 @@
+using System;
+
+using Sharprompt.Drivers;
+
+using Xunit;
+
+namespace Sharprompt.Tests;
+
+public class ConsoleDriverFactoryTests
+{
+    [Fact]
+    public void ConsoleDriverFactory_DefaultFactory_IsNotNull()
+    {
+        Assert.NotNull(Prompt.ConsoleDriverFactory);
+    }
+
+    [Fact]
+    public void ConsoleDriverFactory_SetCustomFactory_ReturnsCustomFactory()
+    {
+        var originalFactory = Prompt.ConsoleDriverFactory;
+
+        try
+        {
+            var customDriver = new StubConsoleDriver();
+            Prompt.ConsoleDriverFactory = () => customDriver;
+
+            var driver = Prompt.ConsoleDriverFactory();
+
+            Assert.Same(customDriver, driver);
+        }
+        finally
+        {
+            Prompt.ConsoleDriverFactory = originalFactory;
+        }
+    }
+
+    [Fact]
+    public void ConsoleDriverFactory_SetNull_ThrowsArgumentNullException()
+    {
+        Assert.Throws<ArgumentNullException>(() => Prompt.ConsoleDriverFactory = null!);
+    }
+
+    [Fact]
+    public void ConsoleDriverFactory_AfterReset_ReturnsPreviousFactory()
+    {
+        var originalFactory = Prompt.ConsoleDriverFactory;
+
+        try
+        {
+            Prompt.ConsoleDriverFactory = () => new StubConsoleDriver();
+
+            Prompt.ConsoleDriverFactory = originalFactory;
+
+            Assert.Same(originalFactory, Prompt.ConsoleDriverFactory);
+        }
+        finally
+        {
+            Prompt.ConsoleDriverFactory = originalFactory;
+        }
+    }
+
+    [Fact]
+    public void IConsoleDriver_CustomImplementation_CanBeAssigned()
+    {
+        var originalFactory = Prompt.ConsoleDriverFactory;
+
+        try
+        {
+            IConsoleDriver driver = new StubConsoleDriver();
+            Prompt.ConsoleDriverFactory = () => driver;
+
+            var result = Prompt.ConsoleDriverFactory();
+
+            Assert.IsAssignableFrom<IConsoleDriver>(result);
+            Assert.Same(driver, result);
+        }
+        finally
+        {
+            Prompt.ConsoleDriverFactory = originalFactory;
+        }
+    }
+
+    private sealed class StubConsoleDriver : IConsoleDriver
+    {
+        public void Dispose() { }
+        public void Beep() { }
+        public void Reset() { }
+        public void ClearLine(int top) { }
+        public ConsoleKeyInfo ReadKey() => new('\0', ConsoleKey.Enter, false, false, false);
+        public void Write(string value, ConsoleColor color) { }
+        public void WriteLine() { }
+        public void SetCursorPosition(int left, int top) { }
+        public bool KeyAvailable => false;
+        public bool CursorVisible { set { } }
+        public int CursorLeft => 0;
+        public int CursorTop => 0;
+        public int BufferWidth => 80;
+        public int BufferHeight => 24;
+        public int WindowWidth => 80;
+        public int WindowHeight => 24;
+        public Action CancellationCallback { get; set; } = () => { };
+    }
+}