When a coaster is under construction, it is in the act of being built. When a coaster starts to go through construction, it starts with careful planning. Then, they start building supports. Adding the track comes right after the supports. The coaster then starts to go under testing. They start with using dummies, making sure the ride is safe. After they tested the ride ample times with dummies, they use actual humans. Usually, even if a roller coaster has finished construction stages and has gone into testing, It will still be classed as Under Construction until it opens.