Recently I wrote a small blog entry
Why to cars have brakes?
It's getting a lot of hits. Well, a lot for me. So naturally in my quest for even more hits here's a follow up...
Imagine you're in a car. Driving along. Why do you brake? I'm not asking what happens when you press the brake pedal? That's too easy (the car stops). I'm asking why…?
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Here are two reasons:
Reason one: because there's danger ahead
This corresponds to a failing test. More specifically, it's when a test runs and asserts. A red. Perhaps there's a queue of traffic ahead (often a problem on the orbital car park known as the M25). Perhaps the road is closed off because workmen are working on it. Or maybe the local council has been meddling and the road is now a one-way-but-not-the-way-you-want-to-go road. Whatever the reason, something is not as expected.
Reason two: because you've arrived!
This corresponds to a passing test. A green. Wherever it is you're going, you've got there. Nothing unexpected happened. No traffic queues. No closed off roads. No meddling local council. Incredible!
In my entirely unscientific sampling almost everyone answers with the first reason. The second reason is not nearly as common. I find this interesting. I think maybe it's a reflection of the thinking statically vs thinking dynamically thing again. A perception that tests are most useful when they fire red. That tests which run to completion without incident are not so useful. But they are. Maybe more so.
Brakes help me stop. And stopping implies I'm already moving - I'm already going somewhere. But where? If I don't know where I'm going why am I moving at all? If I don't know where I'm going I'm just as lost as if I don't know where I am.
Tests are useful not just because of the I-didn't-arrive effect when they fail, they're also useful because of the I-did-arrive effect when they pass.
Another reason passing tests are really useful is the elves. But the elves will have to wait for another time.
