In any complex creative endeavour – and, yes, software development is a creative endeavour – feedback is essential to getting it right (or, at least, less wrong).
The best development approaches tend to be built around feedback loops, and the last few decades of innovation in development practices and processes have largely focused on shrinking those feedback loops so we can learn our way to Better faster.
When we test our software, that’s a feedback loop, for example. Although far less common these days, there are still teams out there doing it manually. Their testing feedback loops can last days or even weeks. Many teams, though, write fast-running automated tests, and can test the bulk of their code in minutes or even seconds.
What difference does it make if your tests take days instead of seconds?
To illustrate, I’m going to draw a parallel with movie production. Up until the late 1960s, feedback loops in movie making were at best daily. Footage shot on film during the day were processed by a lab and then watched by directors, producers, editors and so on at the end of the day. Hence the movie industry term “dailies”. If a shot didn’t come out right – maybe the performance didn’t fit into the context of that scene with a previous scene (the classic “boom microphone in shot” or “character just ran 6 miles but is mysteriously not out of breath” spring to mind) – chances are the production team wouldn’t know until they saw the footage later.
That could well mean going back and reshooting some scenes. That means calling back the actors and the crew, and potentially remounting the whole thing if the sets have already been pulled down. Expensive. Sometimes prohibitively expensive, which is why lower-budget productions had little choice but to keep those shots in their theatrical releases.
In the 1960s, comedy directors like Jerry Lewis and Blake Edwards pioneered the use of Video assist. These were systems that enabled the same footage to be recorded simultaneously on film and on videotape, so actors and directors could watch takes back as soon as they’d been captured, and correct mistakes there and then when the actors, crew, sets and so on were all still there. Way, way cheaper than remounting.
The speed of testing feedback in software development has a similar impact. If I make a change that breaks the code, and my code is tested overnight, say, then I probably won’t know it’s broken until the next day (or the next week, or the next month, or the next year when a user reports the bug).
But I’ve already moved on. The sets have been dismantled, so to speak. To fix a bug long after the fact requires the equivalent of remounting a shoot in movies. Time has to be scheduled, the developer has to wrap their head around that code again, and the bug fix has to go through the whole testing and release process again. Far more expensive. Often orders of magnitude more expensive. Sometimes prohibitively expensive, which is why many teams ship software they know has bugs, but they just don’t have budget to fix them (or, at least, they believe they’re not worth fixing.)
If my code is tested in seconds, that’s like having Video assist. I can make one change and run the tests. If I broke the code, I’ll know there and then, and can easily fix it while I’m still in the zone.
Just as Video assist helps directors make better movies for less money, fast-running automated tests can help us deliver more reliable software with less effort. This is a measurable effect (indeed, it has been measured), so we know it works.