Help debugging a test based on `<nixpkgs/nixos/tests/installer.nix>`

Hey,

Id like to test installation with nixos-anywhere inside nixos tests.

I’ve followed closely a similar test from nixos-anywhere repository. I updated the test as needed to keep up with changes to the nixos test driver, but kept the qemu command line args the same.

The test is supposed to run installation from one nixos test machine to another. After the installation it’s supposed to boot the just installed machine again with qemu and do some check on that machine.
Here is the test, reproduce with nix build github:mlabs-haskell/spo-anywhere/22ee919\#checks.x86_64-linux.testing-install-script.

Installation seemingly succeeds but then it looks like the booting of the machine the second time never finishes and the test timeouts after an hour.

My problem is how to fix this, but even more so - how to debug this?
It looks like I’m not getting any output from qemu. The boot process might fail in seconds and im not getting any debug info about that. How would I debug what happens in the installed machine after new_machine.start() line?

The test output is available in files: install_script_stdout.log and install_script_stderr.log.

Thanks!