I've worked in start ups where they don't have automated tests.

The code quality is not as good. But that imo is not a symptom of lack of tests. It's a symptom of being a start up and the desire to move fast.

As for mysterious error or bugs that occur the rate at which we get them in the code is no larger than code with tests.

It turns out that manual testing and static checking is mostly enough.

I think for most stuff testing is an illusion. It's one of those faith based mantras developers follow without any basis in science. There are a few applications where I feel automated tests are required but they are not the majority of software projects.

I've worked in plenty too. They start out faster. Delivery and quality both decrease almost imperceptibly for a long period. When somebody who understood how everything was built leaves because they got offered 20% more elsewhere, delivery and quality both plunge quite a lot and the decline accelerates.

It's incredibly unusual for them to recover delivery speed and quality after not doing automated testing for so long. It's incredibly hard to "bolt on" testing afterwards - both because the culture and context isn't there but also because the tooling and infrastructure can't be built up in a week. Most companies in this state look for quick fixes like:

* Elaborate branching strategies

* Entirely different versions of the software for different clients (because you're too afraid to upgrade them all).

* Ever more infrequent releases.

The next step is technical bankruptcy. That's when your devs start whingeing about wanting to do a full rewrite. That's usually the point where you've probably ended up losing money overall by dodging tests.

It can work without tests you manage to hit product/market fit before the decline sets in, but I find that companies in this situation often tend to struggle developing and will often stagnate. 1/50 might tap into some undiscovered new market opportunity and hit it out of the park either way but it's rare.

> It's a symptom of being a start up and the desire to move fast.

My take is that you can only move fast when you are not in a hurry. If you are in a hurry, you need to work slower, or things will be messed up with no time to fix it.

Thus, usually, there is no need to move fast, since if you can, you are not in a hurry anyway.