This is a test instance of Wikidata. It is not the same as the production website. It is also not a generic MediaWiki testing site: Please use the test instance of Wikipedia (or the secondary test instance) for that. For more advanced testing, you may want to simply set up your own copy of MediaWiki and install Wikibase. Happy testing!!!
The Wikidata Test Wiki is for developers to test their code without breaking all of Wikimedia, and blowing the world up.
The Wikidata Test Wiki may also be used in a classroom environment for teaching basic Wikidata editing to avoid the great confusion resulting from creating pages and breaking a regular project, although this may not always be desirable because of the occasional difference between the test interface and a typical Wikimedia project interface.