@Override
 protected Contact getContactForEnterRangeEvent(Sensor sensor, Mover target) {
   Contact contact = contacts.get(target);
   if (contact == null) {
     contact = new SensorContact((Mover) target);
     contacts.put(target, contact);
   }
   System.out.println(
       "TestMediator providing contact "
           + contact.toString()
           + " for target "
           + target.toString());
   return contact;
 }