Why are automated tests worth the trouble?

Imagine a factory line where a machine puts holes in sheets of steel. These holes need to be a specific size and shape to house bolts for the finished product. The designer of the factory line will set up the machine, test the holes, and move on. Eventually, something will change: the steel might be thicker, a worker could adjust the hole size, or more holes may need to be punched because the design has changed. A smart designer will install quality control checks at key points to ensure that the product meets the specifications. It doesn’t matter how the holes are made: drilled, punched, or laser cut, they must meet certain requirements.

The same principle applies to software development. It’s hard to predict which code will remain stable for years and which will undergo multiple revisions. As software functionality expands, we must ensure that we don’t inadvertently break things. And we will make mistakes. Even...