How to Undo a bool on an EditorWindow

I have been tackling this issue for a while but I cant get any results. I get the "Happened" messaged on the console, and if I go to the Edit>Undo, i see "testing" after it, meaning it recorded the change.

But when I press it, or do Ctrl-Z nothing happens. The bool testing has to be public and static because I also want to change her throght a MenuItem.

I have tried multiple approaches this was one of them

     using UnityEngine;
     using System.Collections;
     using UnityEditor;
    
     public class MapMaker2D : EditorWindow {
 
         //instance of this script
         public static MapMaker2D instance;
        
         //testbool
         public static bool testing;
     
         //runs whenever the window is created
         void OnEnable()
         { 
             //sets instance of mapmaker
             instance = this;
          }
     
     void OnGUI()
         {
                    EditorGUI.BeginChangeCheck ();
     
             bool atesting=EditorGUILayout.Toggle (new GUIContent("testing","testing variable"),testing);
             if (EditorGUI.EndChangeCheck ()) {
     
                 Debug.Log ("Happened");
     
                 Undo.RegisterCompleteObjectUndo(this, "testing");
                 testing=atesting;
             }
           }
     }