Board Thread:Support Requests - Community Management/@comment-43368626-20191121210855/@comment-34888194-20191121211341

You can create your own sandbox in your user subpage. Just go to Special:Mypage/Sandbox and you can use that subpage as your sandbox.

Also, there's really no official way to name your testing page. It's generally preferred to use  or   or something similar to that so others will know that is your testing page.