Mark - thanks for your reply. I'd lean towards 3 as it's closest to my live environment. However, I have two concerns/questions:
1 any chance that google would see it as duplicate of your site? Maybe that's handled with a blocked agent in the .htaccess of the backup/testing site
2 which is really about my lazyness - does this require that you manually take a backup then install and configure it before testing, or does akeeba offer some automation for "cloning" sites?
You can clone your site anywhere using akeeba backup and akeeba kickstart.
You have three main choices as to where...
1. do your testing locally (not ideal as server settings might not be the same)
2. do you testing in a subfolder of you production site
3. create a subdomain on you main domain
My preference is to use 3 - but I do 1 and 2 also.