In reply to @hexa:lossy.network
https://logs.nix.ci/?key=nixos/nixpkgs.127091&attempt_id=f0ef90c3-3a50-44be-b36c-eeb97f7ddd1f

def assemble_qemu_flags():
    flags = "-cpu max"
    flags += " -m 1024"
    return flags


qemu_flags = {"qemuFlags": assemble_qemu_flags()}

hd_flags = {
    "hdaInterface": "virtio",
    "hda": "vm-state-machine/machine.qcow2",
}

default_flags = {**hd_flags, **qemu_flags}


def create_machine_named(name):
    return create_machine({**default_flags, "name": name})


machine.start()

with subtest("Assert readiness of login prompt"):
    machine.succeed("echo hello")

with subtest("Wait for hard disks to appear in /dev"):
    machine.succeed("udevadm settle")

machine.succeed(
    "sgdisk -Z /dev/vda",
    "sgdisk -n 1:0:+1M -n 2:0:+1G -N 3 -t 1:ef02 -t 2:8200 -t 3:8300 -c 3:root /dev/vda",
    "mkswap /dev/vda2 -L swap",
    "swapon -L swap",
    "mkfs.btrfs -L root /dev/vda3",
    "btrfs device scan",
    "mount LABEL=root /mnt",
    "btrfs subvol create /mnt/boot",
    "btrfs subvol create /mnt/nixos",
    "btrfs subvol create /mnt/nixos/default",
    "umount /mnt",
    "mount -o defaults,subvol=nixos/default LABEL=root /mnt",
    "mkdir /mnt/boot",
    "mount -o defaults,subvol=boot LABEL=root /mnt/boot",
)


with subtest("Create the NixOS configuration"):
    machine.succeed("nixos-generate-config --root /mnt")
    machine.succeed("cat /mnt/etc/nixos/hardware-configuration.nix >&2")
    machine.copy_from_host(
        "/nix/store/jmypyz7q2ffcqg0dfa9xydz4wap04wsp-configuration.nix",
        "/mnt/etc/nixos/configuration.nix",
    )

with subtest("Perform the installation"):
    machine.succeed("nixos-install < /dev/null >&2")

with subtest("Do it again to make sure it's idempotent"):
    machine.succeed("nixos-install < /dev/null >&2")

with subtest("Shutdown system after installation"):
    machine.succeed("umount /mnt/boot || true")
    machine.succeed("umount /mnt")
    machine.succeed("sync")
    machine.shutdown()
# Now see if we can boot the installation.
machine = create_machine_named("boot-after-install")

# For example to enter LUKS passphrase.


with subtest("Assert that /boot get mounted"):
    machine.wait_for_unit("local-fs.target")
    machine.succeed("test -e /boot/grub")

with subtest("Check whether /root has correct permissions"):
    assert "700" in machine.succeed("stat -c '%a' /root")

with subtest("Assert swap device got activated"):
    # uncomment once https://bugs.freedesktop.org/show_bug.cgi?id=86930 is resolved
    machine.wait_for_unit("swap.target")
    machine.succeed("cat /proc/swaps | grep -q /dev")

with subtest("Check that the store is in good shape"):
    machine.succeed("nix-store --verify --check-contents >&2")

with subtest("Check whether the channel works"):
    machine.succeed("nix-env -iA nixos.procps >&2")
    assert ".nix-profile" in machine.succeed("type -tP ps | tee /dev/stderr")

with subtest(
    "Check that the daemon works, and that non-root users can run builds "
    "(this will build a new profile generation through the daemon)"
):
    machine.succeed("su alice -l -c 'nix-env -iA nixos.procps' >&2")

with subtest("Configure system with writable Nix store on next boot"):
    # we're not using copy_from_host here because the installer image
    # doesn't know about the host-guest sharing mechanism.
    machine.copy_from_host_via_shell(
        "/nix/store/6jcfa0im2sjsyhzbqgz51w6hwqhgd7x4-configuration.nix",
        "/etc/nixos/configuration.nix",
    )

with subtest("Check whether nixos-rebuild works"):
    machine.succeed("nixos-rebuild switch >&2")

with subtest("Test nixos-option"):
    kernel_modules = machine.succeed("nixos-option boot.initrd.kernelModules")
    assert "virtio_console" in kernel_modules
    assert "List of modules" in kernel_modules
    assert "qemu-guest.nix" in kernel_modules

machine.shutdown()

# Check whether a writable store build works
machine = create_machine_named("rebuild-switch")

machine.wait_for_unit("multi-user.target")

# we're not using copy_from_host here because the installer image
# doesn't know about the host-guest sharing mechanism.
machine.copy_from_host_via_shell(
    "/nix/store/v25vc36mamldkz4f067nyfy1z15r12g1-configuration.nix",
    "/etc/nixos/configuration.nix",
)
machine.succeed("nixos-rebuild boot >&2")
machine.shutdown()

# And just to be sure, check that the machine still boots after
# "nixos-rebuild switch".
machine = create_machine_named("boot-after-rebuild-switch")

machine.wait_for_unit("network.target")

machine.shutdown()

# Tests for validating clone configuration entries in grub menu

gives:

Traceback (most recent call last):
  File "/nix/store/rbdw7qvz9bga3k4h0p3awh5xkkh5p7ax-nixos-test-driver/bin/.nixos-test-driver-wrapped", line 1050, in <module>
    run_tests(args.interactive)
  File "/nix/store/rbdw7qvz9bga3k4h0p3awh5xkkh5p7ax-nixos-test-driver/bin/.nixos-test-driver-wrapped", line 931, in run_tests
    test_script()
  File "/nix/store/rbdw7qvz9bga3k4h0p3awh5xkkh5p7ax-nixos-test-driver/bin/.nixos-test-driver-wrapped", line 1020, in test_script
    exec(pathlib.Path(args.testscript).read_text())
  File "<string>", line 68, in <module>
  File "<string>", line 18, in create_machine_named
NameError: name 'default_flags' is not defined