I have a few websites that I need to move to a new server - how would I test that they work before switching DNS? What URL would I navigate to?
The easiest way is to modify your hosts file to hardcode the domain name to the new IP address temporarily. See this guide for OS-specific instructions. Don't forget to remove the entry again after you're done testing.
Alternatively, you could setup a temporary test subdomain for each site on the new server (