I Define 2 sites for this task instead of 1: mainsite & testsite. Then I set both sites to the same local folder.
Doing it this way there is no to fill in the testing server info in Dreamweaver; I just fill in the local and remote.
This allows me to right click and put the file(s) &/or folder(s) to either mainsite or testsite by simply toggling between them with the drop down in the files pallet. I can also 'save to remote server', but I tend to favor 'put' as it seems fifty times faster on every site I've worked on.
Let me know what version you are using & server type/info if the above doesn't work