There are 2 issues in the MwApiContentProvider class in /content-providers/ which 1 will affect testing the class and the other is just an improvement.

1. Wrapping the call to file_get_contents() so it can be stubbed and using MediaWikiServices HttpRequestFactory class to make an HTTP request. The benefit of this is; the class will be easily testable and data can easily be injected (DI) during tests. Also, will avoid the use of suppressing warnings and all that messy stuff :)

2. The use of MediaWiki's JSON Formatter class, FormatJson::decode() instead of json_decode() which is generally advised to be used; https://doc.wikimedia.org/mediawiki-core/master/php/classFormatJson.html.

This minor refactoring will improve on the over all functionality and efficiency of the code and provides an easy way of testing this class.