The WMF Community Tech team runs a Cloud VPS instance at http://commtech.wmflabs.org/. This instance is used for testing any MediaWiki related work that is too risky to test in a production environment.
To access commtech.wmflabs.org, ssh to
commtech-1.commtech.eqiad.wmflabs. (If this doesn't work for you, make sure your proxy settings are correct.) The wiki installation is located in the
/srv/mediawiki-vagrant directory on that server. Note that it is a MediaWiki-Vagrant installation.