SpaceX has finished testing three first stage cores for its Falcon Heavy rocket. The testing was carried out at its McGregor, Texas facility and the process started back in May. All of this work is leading up to an actual launch of the rocket, which is essentially three Falcon 9 rockets joined together.
With the Falcon Heavy, SpaceX will be able to carry much larger payloads to space. The Heavy can bring up to 140,700 lbs, drastically more than the Falcon 9's 50,000 lbs.
SpaceX publicly revealed the Falcon Heavy in 2011.