Practice mode (sandbox mode)

I mentioned why there isn't a practice mode because when i want to try something new (skills , tricks , mechanics , etc.) its really hard because of the long CD of spells . For example if i try R+F with lee sin and i fail i need to wait 5 minutes or other skills with other champs that requires a specific positioning of the enemy . Yes , i know that I can invite a friend to help me but not at any time my friends are able to . I want to say that will be great to be created this "Practice mode " and that will help to many players to try everything that they want to learn , instead of going on normal games , to fail and their teammates to blame them . ( Sorry if i wrote something wrong here , eng isnt my first lang. )