WHAT IS A SMOKE TEST AND WHY IT IS PERFORMED?????

A SMOKE TEST IS USED TO FIND A VACCUM LEAK OR A LEAK IN THE INTAKE IT IS DONE BY PUMPING SMOKE INTO THE CAR. ITS A SIMPLE WAY TO FIND THE LEAK AND ITS CHEAPER. THE OTHER OPTION IS TO TAKE THE EMISSIONS SYSTEM APART AND THE LABOR FOR THAT COULD BE IN THE THOUSANDS! MOST COMMON SITUATIONS WE DO A SMOKE TEST IS FOR P0420 BUT THERE IS MANY OTHER USES MOST SHOPS CHARGE 1 HOUR BUT THERE IS SOME OUT THERE THAT CHARGE BY THE ACTUAL TIME IT TAKES TO FIND THE ISSUE