Ideas of things to scan for:
* Any request resulting in an error response (404 Not Found, 500 Internal Error, etc.).
* Uncaught JavaScript exceptions.
* Network requests made to third-party domains (images, stylesheets, scripts, xhr, etc.)
From comment 13 at {T71445} :
> However it would be great to have automated tests running after changes in common.js and gadgets. Such general tests can at least validate no external resource is loaded, or no invalid syntax is added.
> The simplest option is to run it outside MW (such as a script in labs that runs X times a day), but an extension to do it while editing would be even better...
>
> BTW
> I just runned a simple phantomjs script on all wikipedia languages to catch simple errors:
>
> testing als
> ERROR: ReferenceError: Can't find variable: ta
> TRACE:
> -> https://als.wikipedia.org/w/index.php?title=MediaWiki:If-pt-login.js&action=raw&ctype=text/javascript&dontcountme=s: 9
>
> testing kk
> ERROR: TypeError: 'null' is not an object (evaluating 'document.getElementById('mw-vector-current-variant').innerHTML=wgULS("Кирил","Latın","توتە")')
> TRACE:
> -> https://bits.wikimedia.org/kk.wikipedia.org/load.php?debug=false&lang=kk&modules=site&only=scripts&skin=vector&*: 9
>
>
> anyone wants to fix them? :)
>
From comment 14 at T71445:
> Example for errors across wikis
> Maybe it is a bit off-topic but here are some cases of errors across wikis in simple read/edit transaction using phantomJS