diff --git a/Terminal.Gui/App/Application.Run.cs b/Terminal.Gui/App/Application.Run.cs
index d6dbb6728..0fbda40aa 100644
--- a/Terminal.Gui/App/Application.Run.cs
+++ b/Terminal.Gui/App/Application.Run.cs
@@ -398,7 +398,11 @@ public static partial class Application // Run (Begin -> Run -> Layout/Draw -> E
     ///     Set to true to cause <see cref="End"/> to be called after the first iteration. Set to false (the default) to
     ///     cause the application to continue running until Application.RequestStop () is called.
     /// </summary>
-    public static bool EndAfterFirstIteration { get; set; }
+    public static bool EndAfterFirstIteration
+    {
+        get => ApplicationImpl.Instance.EndAfterFirstIteration;
+        set => ApplicationImpl.Instance.EndAfterFirstIteration = value;
+    }
 
     /// <summary>Building block API: Runs the main loop for the created <see cref="Toplevel"/>.</summary>
     /// <param name="state">The state returned by the <see cref="Begin(Toplevel)"/> method.</param>
diff --git a/Terminal.Gui/App/Application.Screen.cs b/Terminal.Gui/App/Application.Screen.cs
index 3804c19c7..920dec1fa 100644
--- a/Terminal.Gui/App/Application.Screen.cs
+++ b/Terminal.Gui/App/Application.Screen.cs
@@ -23,12 +23,31 @@ public static partial class Application // Screen related stuff; intended to hid
     ///     Event handlers can set <see cref="SizeChangedEventArgs.Cancel"/> to <see langword="true"/> to prevent
     ///     <see cref="Application"/> from changing it's size to match the new terminal size.
     /// </remarks>
-    public static event EventHandler<SizeChangedEventArgs>? SizeChanging;
+    public static event EventHandler<SizeChangedEventArgs>? SizeChanging
+    {
+        add
+        {
+            if (ApplicationImpl.Instance is ApplicationImpl impl)
+            {
+                impl.SizeChanging += value;
+            }
+        }
+        remove
+        {
+            if (ApplicationImpl.Instance is ApplicationImpl impl)
+            {
+                impl.SizeChanging -= value;
+            }
+        }
+    }
 
     // Internal helper method for ApplicationImpl.ResetState to clear this event
     internal static void ClearSizeChangingEvent ()
     {
-        SizeChanging = null;
+        if (ApplicationImpl.Instance is ApplicationImpl impl)
+        {
+            impl.SizeChanging = null;
+        }
     }
 
     /// <summary>
@@ -39,24 +58,7 @@ public static partial class Application // Screen related stuff; intended to hid
     /// <returns><see lanword="true"/>if the size was changed.</returns>
     public static bool OnSizeChanging (SizeChangedEventArgs args)
     {
-        SizeChanging?.Invoke (null, args);
-
-        if (args.Cancel || args.Size is null)
-        {
-            return false;
-        }
-
-        Screen = new (Point.Empty, args.Size.Value);
-
-        foreach (Toplevel t in TopLevels)
-        {
-            t.OnSizeChanging (new (args.Size));
-            t.SetNeedsLayout ();
-        }
-
-        LayoutAndDraw (true);
-
-        return true;
+        return ApplicationImpl.Instance.OnSizeChanging (args);
     }
 
     /// <summary>
diff --git a/Terminal.Gui/App/ApplicationImpl.cs b/Terminal.Gui/App/ApplicationImpl.cs
index 5b6809ee5..d6cf56a53 100644
--- a/Terminal.Gui/App/ApplicationImpl.cs
+++ b/Terminal.Gui/App/ApplicationImpl.cs
@@ -128,6 +128,9 @@ public class ApplicationImpl : IApplication
     /// <inheritdoc/>
     public bool ClearScreenNextIteration { get; set; }
 
+    /// <inheritdoc/>
+    public bool EndAfterFirstIteration { get; set; }
+
     /// <inheritdoc/>
     public ApplicationPopover? Popover { get; set; }
 
@@ -157,6 +160,11 @@ public class ApplicationImpl : IApplication
         }
     }
 
+    /// <summary>
+    ///     This event is raised when the application's size changes.
+    /// </summary>
+    public event EventHandler<SizeChangedEventArgs>? SizeChanging;
+
     /// <inheritdoc/>
     public void RequestStop () { RequestStop (null); }
 
@@ -421,6 +429,29 @@ public class ApplicationImpl : IApplication
         _driver?.Refresh ();
     }
 
+    /// <inheritdoc/>
+    public bool OnSizeChanging (SizeChangedEventArgs args)
+    {
+        SizeChanging?.Invoke (null, args);
+
+        if (args.Cancel || args.Size is null)
+        {
+            return false;
+        }
+
+        Screen = new (Point.Empty, args.Size.Value);
+
+        foreach (Toplevel t in TopLevels)
+        {
+            t.OnSizeChanging (new (args.Size));
+            t.SetNeedsLayout ();
+        }
+
+        LayoutAndDraw (true);
+
+        return true;
+    }
+
     /// <inheritdoc/>
     public void ResetState (bool ignoreDisposed = false)
     {
@@ -463,9 +494,9 @@ public class ApplicationImpl : IApplication
 
         MainThreadId = -1;
 
-        // These static properties need to be reset
-        Application.EndAfterFirstIteration = false;
-        Application.ClearScreenNextIteration = false;
+        // Reset iteration flags
+        EndAfterFirstIteration = false;
+        ClearScreenNextIteration = false;
 
         // Driver stuff
         if (_driver is { })
@@ -488,12 +519,12 @@ public class ApplicationImpl : IApplication
         // Do not clear _lastMousePosition; Popovers require it to stay set with
         // last mouse pos.
         //_lastMousePosition = null;
-        Application.CachedViewsUnderMouse.Clear ();
-        Application.ResetMouseState ();
+        Mouse.CachedViewsUnderMouse.Clear ();
+        Mouse.ResetState ();
 
         // Keyboard events and bindings are now managed by the Keyboard instance
 
-        Application.ClearSizeChangingEvent ();
+        SizeChanging = null;
 
         Navigation = null;
 
@@ -623,11 +654,11 @@ public class ApplicationImpl : IApplication
         return new MainLoopCoordinator<T> (_timedEvents, inputBuffer, loop, cf);
     }
 
-    private void Driver_KeyDown (object? sender, Key e) { Application.RaiseKeyDownEvent (e); }
-    private void Driver_KeyUp (object? sender, Key e) { Application.RaiseKeyUpEvent (e); }
-    private void Driver_MouseEvent (object? sender, MouseEventArgs e) { Application.RaiseMouseEvent (e); }
+    private void Driver_KeyDown (object? sender, Key e) { Keyboard.RaiseKeyDownEvent (e); }
+    private void Driver_KeyUp (object? sender, Key e) { Keyboard.RaiseKeyUpEvent (e); }
+    private void Driver_MouseEvent (object? sender, MouseEventArgs e) { Mouse.RaiseMouseEvent (e); }
 
-    private void Driver_SizeChanged (object? sender, SizeChangedEventArgs e) { Application.OnSizeChanging (e); }
+    private void Driver_SizeChanged (object? sender, SizeChangedEventArgs e) { OnSizeChanging (e); }
 
     private static List<CultureInfo> GetAvailableCulturesFromEmbeddedResources ()
     {
diff --git a/Terminal.Gui/App/IApplication.cs b/Terminal.Gui/App/IApplication.cs
index a2777327b..65332c23d 100644
--- a/Terminal.Gui/App/IApplication.cs
+++ b/Terminal.Gui/App/IApplication.cs
@@ -27,6 +27,14 @@ public interface IApplication
     /// <summary>Gets or sets the console driver being used.</summary>
     IConsoleDriver? Driver { get; set; }
 
+    /// <summary>
+    ///     This is intended for unit tests and won't stop the <see cref="Application.RunLoop"/> if set to <see langword="true"/>
+    ///     If the caller calls <see cref="Application.RunLoop"/> with the returned token from <see cref="Application.Begin"/>, setting
+    ///     this property to <see langword="true"/> will cause only one iteration of the main loop to execute. The default is
+    ///     <see langword="false"/>, which will cause the application to continue running until Application.RequestStop () is called.
+    /// </summary>
+    bool EndAfterFirstIteration { get; set; }
+
     /// <summary>
     ///     Gets or sets whether <see cref="Driver"/> will be forced to output only the 16 colors defined in
     ///     <see cref="ColorName16"/>. The default is <see langword="false"/>, meaning 24-bit (TrueColor) colors will be output
@@ -101,6 +109,14 @@ public interface IApplication
     /// </param>
     public void LayoutAndDraw (bool forceRedraw = false);
 
+    /// <summary>
+    ///     Called when the application's size changes. Sets the size of all <see cref="Toplevel"/>s and fires the
+    ///     SizeChanging event.
+    /// </summary>
+    /// <param name="args">The new size.</param>
+    /// <returns><see langword="true"/> if the size was changed.</returns>
+    bool OnSizeChanging (SizeChangedEventArgs args);
+
     /// <summary>
     ///     Maximum number of iterations of the main loop (and hence draws)
     ///     to allow to occur per second. Defaults to <see cref="Application.DEFAULT_MAXIMUM_ITERATIONS_PER_SECOND"/> which is