Some classes on the SOWISO platform are used exclusively for testing, and not for any other learning. Hence, it's not needed to show anything else to the students in that class than scheduled tests.
To do so, go the the "Teacher" menu and click "Settings", the first setting is the "Class mode" where you can select "Testing only".
It's always possible to change this setting, it does not interfere with other class settings. For example: you can change the setting to "Testing only" during an exam day, and after that day you can change it back to "Practicing and testing" again.