No programmer ever releases a software without having tested it – even for the most basic proof of concept and rough hack, the developer will run it once to see that it at least starts and resembles what they had in mind.

But to test, as a verb, usually ends up meaning clicking buttons here and there to get a vague sense of confidence that the software does what we intended. This is different from test as a noun, which means a set of written-out checks that our software must pass to confirm it does what we wanted.

Apart from being more reliable, written-out checks force us to think about what the code must do. They force us to get into the details and think beforehand about what we want to build. Otherwise, we would just jump to building without thinking about what we are building. And trying to ensure that what gets built...