PHPunit 9 & more test unification (#28)

* Start toward phpunit 9 WIP though...

* There are no integration tests in datamodel

Author: addwiki-ci

composer.json

@@ -18,7 +18,7 @@
     "require-dev": {
         "jakub-onderka/php-parallel-lint": "^0.9.2",
         "mediawiki/mediawiki-codesniffer": "~34.0",
-        "phpunit/phpunit": "~8"
+        "phpunit/phpunit": "~9"
     },
     "suggest": {
         "etsy/phan": "Allows running static analysis on the package (requires PHP 7+)"