When to test

We are not going to attempt to enlighten every reader to seeing the value of unit testing. The goal of this chapter is to help you figure out where and when you will benefit from using unit testing. Two users may get different benefits from using unit testing, so don't worry about doing everything exactly like the next guy. We will cover the most common value-added scenarios.

Mission critical

When we put tires on our cars, we test the air pressure in those tires. Why do we do this? We do this to make sure that the car has the best chance of getting from point A to point B based on our knowledge of tires. If we had a company put new tires on our car and under-or over-inflate the tires, we would be very upset. They should check this as part of putting new tires on any vehicle. Now when they wash our car, we expect them to do a good job but we don't have quite as high a testing expectation.

This raises the question of testing in software development. How important is testing? Should...