FWIW I develop on Linux and I had to test some of my plugins on Windows. I ended up using the following approach:
- Get Travis-CI to build for Windows as well (here is how I do it)
- When I’m about to release, boot up a Windows VM on Google Cloud with a GPU (I use this image), install Rack+my build on it, and check that it works. It’s not free but testing is pretty quick and billing is per-minute so it’s cheap overall.
HTH