> Is there a build test somewhere, so that this error is checked for automatically?
Unfortunately not. MediaWiki has been getting improved support for PHPUnit and selenium tests over the last year or so, but SMW is not making any use of these facilities AFAIK.
Benedikt Kaempgen, who I cc'd, has been poking at this, you might want to have a chat with him if you are interested in helping out with getting something set up :)
Jeroen De Dauw
Don't panic. Don't be evil.