update CONTRIBUTING.md

Author: simonLeary42

CONTRIBUTING.md

@@ -10,10 +10,10 @@ When submitting pull requests, the pull request should be made to the version yo
 
 This code base is currently using PHP version 7.4. All files are required to be linted with PSR-12 standard. This repository will automatically check PRs for linting compliance.
 
-Whenever frontend JS limits the possible values of a user input, PHP must do the same!
+Whenever frontend JS limits the possible values of a user input, PHP must also do the same, and tests must be written.
 There's nothing stopping a user from making custom HTTP POST requests.
 This can be done in `webroot/panel/*.php` while parsing headers, or preferrably in `resources/lib/*.php`.
-For example, both frontend JS and in the `UnityUser` class make sure that a login shell contains only ASCII characters.
+For example, both frontend JS and in the `UnityUser` class make sure that a login shell contains only ASCII characters, and this is tested in `test/functional/LoginShellSetTest.php`.
 
 ## Development Environment