Fixes #4374 - Nukes all (?) legacy Driver and Application stuff; revamps tests (#4376)

Tests/UnitTests/SetupFakeApplicationAttribute.cs

@@ -0,0 +1,45 @@
+#nullable enable
+using System.Diagnostics;
+using System.Reflection;
+using JetBrains.Annotations;
+using TerminalGuiFluentTesting;
+using Xunit.Sdk;
+
+namespace UnitTests;
+
+/// <summary>
+///     Enables test functions annotated with the [SetupFakeDriver] attribute to set Application.Driver to new
+///     FakeDriver(). The driver is set up with 80 rows and 25 columns.
+/// </summary>
+[AttributeUsage (AttributeTargets.Class | AttributeTargets.Method)]
+public class SetupFakeApplicationAttribute : BeforeAfterTestAttribute
+{
+    private IDisposable? _appDispose = null!;
+    public override void Before (MethodInfo methodUnderTest)
+    {
+        Debug.WriteLine ($"Before: {methodUnderTest.Name}");
+
+        _appDispose?.Dispose ();
+        var appFactory = new FakeApplicationFactory ();
+        _appDispose = appFactory.SetupFakeApplication ();
+
+        base.Before (methodUnderTest);
+    }
+
+    public override void After (MethodInfo methodUnderTest)
+    {
+        Debug.WriteLine ($"After: {methodUnderTest.Name}");
+
+        _appDispose?.Dispose ();
+        _appDispose = null;
+
+        base.After (methodUnderTest);
+    }
+
+    /// <summary>
+    ///     Runs a single iteration of the main loop (layout, draw, run timed events etc.)
+    /// </summary>
+    public static void RunIteration () { ((ApplicationImpl)ApplicationImpl.Instance).Coordinator?.RunIteration (); }
+
+
+}