In a 4.4 site, create a course with one or more forums and all of them have tracking disabled. In the app, login in the site. Open the network inspector and open the course. Check that mod_forum_get_forums_by_courses or core_user_get_users_by_field are NOT called. In browser, enable tracking in one forum. As the student in browser, go to your profile > Forum preferences and disable tracking. In the app, leave the course, go to Preferences and click the Synchronize button to invalidate the cache.  Open the course again. Check that core_user_get_users_by_field is called with the student ID, but mod_forum_get_forums_by_courses is NOT called. As the student in browser, go to your profile > Forum preferences and enable tracking. In the app, leave the course, go to Preferences and click the Synchronize button to invalidate the cache. Open the course again. Check that both core_user_get_users_by_field and mod_forum_get_forums_by_courses are called now. In a 4.3 or older site, the app should behave as it used to: it shouldn't call core_user_get_users_by_field and it will always call mod_forum_get_forums_by_courses.