The Black Spot is one of Susan and Mary's inventions that was first introduced in Johnny on the Spot.
Whatever goes into it exits from another side of it. (example: if someone puts it on a wall and goes inside it, gets out from the other side of the wall) also if it gets ripped into two pieces, whatever gets inside one of its pieces gets out from the other piece. but it has a bug and it is that when it gets ripped apart, after a while, one of its pieces turns into a black hole that can suck the whole earth in it. the only way to deactivate that event is to get a magnetic source to turn the earth's position back to normal.
The girls made it and let Johnny to test it, but got disappointed as soon as they understood that it's only like a door, and with an advice from Johnny, they threw it away. then Johnny took it and had a little fun with it, but as soon as he accidentally ripped it in two pieces (after using it for a magic show), one of the pieces turned into a black hole. with the help of the other piece, the Test kids went to China by placing it on the ground and going to the other side of the earth (China), got the biggest magnetic gun from its miletery and turned the earth back to normal. Susan and Mary attempted to destroy it with laser this time, only unaware that Johnny still kept a small piece of the Black Spot with himself for having fun with it later.