This weekend I stumbled upon a remarkable conversation:

Richard: […] It’s pretty easy to get up to 90 or 95% test coverage. Getting that last 5% is really, really hard and it took about a year for me to get there, but once we got to that point, we stopped getting bug reports from Android. Adam: Oh, wow. Richard: Yeah. IT just worked from there on out. It made a huge, huge difference. We just didn’t really have any bugs for the next eight or nine years.

This is from a conversation with Richard Hipp – the creator of SQLite.

You know what else happened this week? An insane heat wave in the North East of the US (typically an area with “nice” weather). “Jan, you lunatic, what does testing have in common with climate change?”. Bare with me!

Cause Effect
Global warming Portland heat wave
Insufficient testing Bugs never stop

Figuring out causality is hard. Really really hard. Even when we really know the mechanism, it’s just baffling. What’s the cause of this extreme heat wave? It’s caused by global warming. What’s the reason for endless bug reports on my project? It’s insufficient testing.

Once you see it, it won’t stop amusing you. People claiming that anything below 100% test coverage is “practical”, “good”, “pragmatic”. That unit testing to the extreme is dogmatic. Or just complete nonsense like this. Meanwhile the bug reports keep coming, and seemingly never stop. Why would that be?

If you understand the link between climate change and extreme weather events, please consider extending your thinking to other parts of life. Bugs don’t come from nowhere, tests prevent them from happening.