Is this doable?

Is this doable?

I am using wordpress 3.3 for my web site, and I need to upgrade it to version 3.6. I am not sure if I end it up bunch of problem after upgrade. Because I have some custom coding.

So, I was thinking if I am able to create exact copy of the existing wordpress folder under root and name it wordpress2 and use same database (keeping the same wp-config file), I will able to use new “wordpress 2” as a sand box.
It means that I can update the “wordpress2” folder to 3.6 version and see what is actually screw it up and fix it and implement the update on real “wordpress” folder later on. Since I would knew what are the problems, I can fix it right away without having any big mess.

Do you think if that would work? If yes, any tips and tricks?
Thanks,