If you followed steps 1-4 you are creating a new page that’s not in navigation and not being indexed in a new directory(folder) called test.
The only way to get to it would be to have the URL. I don’t know your websites address but it would be something like //https://yourwebsite.com/test/.
Once the test is done you can delete the page from the project and delete the directory on the webserver.
Well, I always assume that people have backups and have a good backup process in place and use it. With something reliable and easy to use like TimeMachine included with the OS, I just make that assumption.
If you don’t have a backup process in place you should get that figured out ASAP. In the meantime, you can always duplicate the project file manually by right-clicking it in finder.
(This might be the same issue as this post @isaiah)