It's easy to write an implementation specific to your existing project's development environment and workflow correctly.
It's hard to write a generic version that works in any environment. It's hard to write a version that lets you build a company and make money.
It's scary to depend on this generic version because it's too generic, and it's built by a for-profit company now who wants to upsell you to some "testcontainer cloud" crap, which doesn't exactly incentivize them to make the OSS version perfect.
For example, we were already using bazel, so writing a version using bazel to create a correct bare rootfs for a dependency + using runc to execute it in tests resulted in something with a roughly 3ms warm startup time that fulfilled all our needs, and cached correctly (since bazel has good caching).
A junior engineer, starry-eyed at test-containers, switched some code over to it, and the warm startup time went up by 1000x from 3ms to 3s, as did the flake-rate, and docker's caching is far worse than bazel's so the several minute cold-starts also happened even more often.
> Testcontainers is exactly the sort of thing open source is great for; it's something where everyone gets to benefit from the wisdom and battle-testing of everyone else.
You get to have a mismatched mess of solutions to everyone's problems, including solution's to problems you don't have. You get code of the quality of the average OSS programmer which, while higher than the average programmer, is still pretty crap.
Free Software is great when it's run by a small group of smart opinionated people. As soon as you try to build a company around that OSS and, god forbid, hire some enterprise sales people and product managers, it quickly becomes worse at the actual small developer problem than what even a mediocre developer could hack out in an hour.
Depending on testcontainers is fine, but if you know what you're doing, writing something purpose-built is fine too, and probably gives you something much nicer in the end.
