Why Are Automated Tests Worth the Trouble?

Imagine a factory line that has a machine putting holes in sheets of steel. These holes have to be of a specific size and shape so that they can house bolts that will hold the finished product together. The designer of such a factory line will set up the machine, test if the holes are correct, and move on. Sooner or later, something will change: the factory will use different, thicker steel; a worker will accidentally change the hole size; or, simply, more holes need to be punched, and the machine has to be upgraded. A smart designer will put quality-control checks at certain points on the line to make sure that the product follows the specification and retains its key qualities. Holes have to conform to particular ...