Johnny Test is more than you think.
Johnny is really a normal preteen boy, when he was 11 he was in a car accident it set his hair on fire and fainted, the ambulance managed to put out the fire and save his life, but he never woke up! Now he lives in his own world. Dukey was his dog, but in real life he never talked, Johnny always wished he would though. Johnny actually only has one older sister named Mary Susan but since she was the last thing he saw before fainting and he was seeing double he is now convinced they are two, his mother died when he was 2, but his father only told him she "went away" that's why she's so busy in the cartoon. Speaking of which his dad was a neat freak in real life but not nearly as much as in the cartoon.
Mary Susan was very smart and good at science, but she did not own a labratory, that was made up by memories of Dexter's Lab, in fact his new family incarnations in his head were loosely based off of Dexter's Lab characters. Bling Bling Boy was made from when Johnny was bored and doodled a picture of Mandark as a gangster.
The reason Johnny is a spoiled brat who gets what he wants most of the time is because he lives in his fantasy world, and let's face it, no one doesn't get what they want in their dreams.
Gil Nextdoor was his neighbor in real life, but his last name was not Nextdoor, Johnny just didn't know what it was and was convinced that was his name as time went on. His sister did have a crush on him, but not as much as her cartoon counterparts, she was too shy to talk to him, that's why he doesn't know the twins in the cartoon.
Johnny will remain in his coma until he dies, which is a long way from now that's why the show's been running so long no matter how bad it is.