nixpkgs/nixos/tests/swap-file-btrfs.nix

import ./make-test-python.nix (
  { lib, ... }:
  {
    name = "swap-file-btrfs";

    meta.maintainers = with lib.maintainers; [ oxalica ];

    nodes.machine =
      { pkgs, ... }:
      {
        virtualisation.useDefaultFilesystems = false;

        virtualisation.rootDevice = "/dev/vda";

        boot.initrd.postDeviceCommands = ''
          ${pkgs.btrfs-progs}/bin/mkfs.btrfs --label root /dev/vda
        '';

        virtualisation.fileSystems = {
          "/" = {
            device = "/dev/disk/by-label/root";
            fsType = "btrfs";
          };
        };

        swapDevices = [
          {
            device = "/var/swapfile";
            size = 1; # 1MiB.
          }
        ];
      };

    testScript = ''
      machine.wait_for_unit('var-swapfile.swap')
      # Ensure the swap file creation script ran to completion without failing when creating the swap file
      machine.fail("systemctl is-failed --quiet mkswap-var-swapfile.service")
      machine.succeed("stat --file-system --format=%T /var/swapfile | grep btrfs")
      # First run. Auto creation.
      machine.succeed("swapon --show | grep /var/swapfile")

      machine.shutdown()
      machine.start()

      # Second run. Use it as-is.
      machine.wait_for_unit('var-swapfile.swap')
      # Ensure the swap file creation script ran to completion without failing when the swap file already exists
      machine.fail("systemctl is-failed --quiet mkswap-var-swapfile.service")
      machine.succeed("swapon --show | grep /var/swapfile")
    '';
  }
)