Unit testing

I've been reading people's opinions of unit testing.

Sean's Boston diaries entry

Response from marginalia

Blurry camcorder footage

> (This is an aside, every single company I've worked for the last 12 years has officially said they were doing "Test Driven Development". To this date, I've *never* seen anyone do this. I'm not even sure it exists outside of textbooks and classroom settings. I've seen more compelling evidence of the Loch Ness-monster than TDD. Please let me know if you have any shaky and blurry camcorder footage of this development practice, I'd love to see it ;-)

[raised hand emoji] I do it sometimes, and I got a job by doing it.

Sometimes

When my Gemini client didn't handle relative URLs correctly, I did some TDD. I knew there was one thing to fix, and I wrote tests for the cases that didn't work. But for some other issue where I'd have to change "this, that and the other thing" - well, then I'd probably try changing this, seeing what effect it has on that, and beating the other thing until it all works. I can't see in advance what the test should be.

Job

When I was looking for work, one company sent me a coding exercise to do in my own time. It was specified that there should be "this thing that does this", and "that thing that does that". So I wrote some tests first, then wrote stuff that made them pass. I got the job. They liked the fact that my code worked not only for the example input in the spec, but for unexpected stuff. Later I saw other people's attempts. No tests at all, and even the example inputs didn't work.

Back in the day

I was amused by the original article that Sean quoted.

Stop mocking your system

> Nothing should ever be mocked. Period. If you don't agree you likely don't understand many things.

I enjoyed the poster's level of confidence in his opinion. As respectfully¹ as possible, I say nonsense. If we want to test A but it uses B and we don't want to set up the big heap of stuff that makes B work, mocking B is what we have to do. I once mocked an entire mainframe. There was a PC system that called the mainframe to do some lookup. There wasn't a spare mainframe available. I mocked the calling code so it popped up a UI dialog to ask the user what the reponse should be. Problem solved, and the other code could be tested.

¹ That's not a sarcastic "respectfully". The poster has a point about isolating the thing that might need mocking. When you think you need a mock, you always have the option to redesign all the code. Of course you'd have much more confidence in that if you have some decent test coverage...

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