Can't upload files

Why do you need a testing server?  Developers who work with server-side code and databases need one that matches their remote server environment. But static HTML sites don't need one.

Testing servers can be really any server.  The difference is that your domain is on the live site but the testing server can have any URL or be on your local machine. If you want to setup a testing server on your local machine, I would recommend MAMP ( https://www.mamp.info/ ) or WAMP ( https://www.wampserver.com/ ).  In these instances your local machine would be your testing server so there would be no need to upload your files.

Go to the Dreamweaver help site:

https://helpx.adobe.com/dreamweaver/user-guide.html

and select Setup Sites: