Garage should fix bikes as part of its docking process (super)
Can't dock bikes if full, release them if empty, or do either if it's not a bike
BikeContainer should know whether it is empty or not
BikeContainer should be able to list its broken bikes
Everything knows what it releases and to what (I have a sinking feeling that they shouldn't....)
BikeContainer should know what its spare capacity is
BikeContainer should be able to stock up on randomly broken bikes
Van should be able to identify what it needs to release to a particular bike container
Van should be able to transfer as much as possible to a garage
Van should be able to transfer as much as possible to a station
Van should be able to complete a transfer with a garage
Van should be able to complete a transfer with a docking station