The series revolves around the adventures of the titular character, Johnny Test, an 11-year-old suburban boy who lives with his parents, his "super-genius" 13-year-old twin sisters, Susan and Mary, who are scientists and best friends with each other, and a talking dog named Dukey. They reside in the fictional town of Porkbelly in North America. Johnny is often used as a test subject for his genius twin sisters' inventions and experiments, ranging from gadgets to superpowers. Their experiments often cause problems that he must resolve, and he must sometimes fight villains in the process. He occasionally saves the world with his sisters' inventions.
