The Testing Gate is the main entrance to the Zoldyck Family's estate. It is guarded by Zebro and consists of seven doors. Each of the 2 panels of the first, smallest door weighs 2 tons, and a bigger panel weighs twice as much as the one immediately preceding it. The doors are designed to open corresponding to the strength of the pushing force. To enter the estate safely, one must open and go through the Testing Gate. Those who enter in any other way will be at risk of being attacked Mike, a huge, trained guard dog of the Zoldyck Family.
Before Killua receives any form of Nen training, he could already open up to the third door, weighing 16 tons in total. Gon, Kurapika and Leorio could also open it after training for just 20 days using Zebro's heavy equipments, and Leorio could even open up to the second door, which weighs 8 tons. Recently, when Killua returns home after the Chimera Ant Extermination mission, he opens the 5th door, weighing 64 tons.