The name of the base class in tests is guaranteed to only occur a
single time in a file. There is not much value in making it relative,
and requiring it to appear in the use section. Especially because it
is in the root namespace.
This reflects what I once encoded in the sniff
https://github.com/wmde/WikibaseCodeSniffer/blob/master/Wikibase/Sniffs/Namespaces/FullQualifiedClassNameSniff.php
I wish we could pick this rule and use it in our codebases. But it
seems it is to specific and can't be applied on all codebases, hence
it can't become part of the upstream MediaWiki rule set. At least not
at the moment.
Change-Id: I77c2490c565b7a468c5c944301fc684d20206ec4