To be safe, creating your own test page is preferred. You can test on that page all you want. But if the page has not been tested on or edited in about a week, other administrators may delete it as an old test page. If you want to help with deleting old test pages, simply click Special:Random and see if it takes you to a test page. If it does, check the history. If it has not been tested on or edited in about a week, delete it as an old test page.