See Vagrant for a more general solution, although you’ll need a plug-in [1] to use qemu.

[1] https://github.com/ppggff/vagrant-qemu

Agree that documentation on qemu is very messy, especially on macOS. (I ran similar experiments with it earlier this year.)

I have been using ubuntu cloud image with cloud-init to achieve something similar, but will try this method as well.

This approach works even better with a firecracker-style linux kernel (faster to start), and with cosmopolitan binaries (so you can do qemu tests not just with linux): a bash cosmopolitan binary is useful if you want to test your bash shell scripts in qemu