The TinkaTester egg is an extremely rare item on Tinkatolli. They can't be traded, and they were an item for closed betas who got all 4 of the previous eggs. It left the island on October 10 2011. It was the fifth of the five beta eggs. It was first hidden on October 4th.
Unlike the other four, this egg was not transparent before being picked up. It was in a different place for everyone.
Many players who recieved the TinkaTester egg put it in their tinkapads. When it is in the bag, it is in the unusuals section.
Over time, it may become Tinkatolli's rarest item.