I actually think that's the point, though: it isn't about testing, it is about not going out of your way to make assumptions. Clearly, your code isn't riddled with #ifdef macOS, or you wouldn't be saying it probably works on Windows. And, as you coded it in Rust using Cargo, as annoying as I may sometimes find their cross compilation behavior, it by and large works: if I take your code I bet I can just ask it to compile for something random, and I'll see what happens... it might even work, and you don't actively know of obvious reason why it can't.

In contrast, a lot of libraries I use--hell: despite myself caring about this, I have become part of the problem (though I'd argue in my defense it is largely because of my dependencies making it hard to even build otherwise)--come with a bespoke build system that only even is able to compile for a handful of targets and where the code is riddled with "ifdef intel elif arm else error" / "ifdef windows elif linux elif apple else error". I can pretty much tell you: my code isn't going to work on anything I didn't develop it for, and would require massive intervention to support something even as trivial sounding as FreeBSD, because none of the parties involved in its code really cared about making it work.

So like, while you might be arguing against the premise, in practice, you could be the poster-child for the movement ;P. You developed your software using an ecosystem that values portability, you didn't go out of your way to undermine such, and you aren't actively poo-pooing people who might want to even try it on other systems (as say every major project from Google, where they either consider a platform to be fully tested and supported or something no one should discuss or even try to fix) you're merely warning them it wasn't tested, and I frankly bet if I showed up with a patch that fixed some unknown issue compiling it for RISC-V you'd even merge the change ;P.