nixos/tests: add swap-partition test

nixos/tests/all-tests.nix

@@ -516,6 +516,7 @@ in {
   step-ca = handleTestOn ["x86_64-linux"] ./step-ca.nix {};
   strongswan-swanctl = handleTest ./strongswan-swanctl.nix {};
   sudo = handleTest ./sudo.nix {};
+  swap-partition = handleTest ./swap-partition.nix {};
   sway = handleTest ./sway.nix {};
   switchTest = handleTest ./switch-test.nix {};
   sympa = handleTest ./sympa.nix {};

nixos/tests/swap-partition.nix

@@ -0,0 +1,48 @@
+import ./make-test-python.nix ({ lib, pkgs, ... }:
+{
+  name = "swap-partition";
+
+  nodes.machine =
+    { config, pkgs, lib, ... }:
+    {
+      virtualisation.useDefaultFilesystems = false;
+
+      virtualisation.bootDevice = "/dev/vda1";
+
+      boot.initrd.postDeviceCommands = ''
+        if ! test -b /dev/vda1; then
+          ${pkgs.parted}/bin/parted --script /dev/vda -- mklabel msdos
+          ${pkgs.parted}/bin/parted --script /dev/vda -- mkpart primary 1MiB -250MiB
+          ${pkgs.parted}/bin/parted --script /dev/vda -- mkpart primary -250MiB 100%
+          sync
+        fi
+
+        FSTYPE=$(blkid -o value -s TYPE /dev/vda1 || true)
+        if test -z "$FSTYPE"; then
+          ${pkgs.e2fsprogs}/bin/mke2fs -t ext4 -L root /dev/vda1
+          ${pkgs.util-linux}/bin/mkswap --label swap /dev/vda2
+        fi
+      '';
+
+      virtualisation.fileSystems = {
+        "/" = {
+          device = "/dev/disk/by-label/root";
+          fsType = "ext4";
+        };
+      };
+
+      swapDevices = [
+        {
+          device = "/dev/disk/by-label/swap";
+        }
+      ];
+    };
+
+  testScript = ''
+    machine.wait_for_unit("multi-user.target")
+
+    with subtest("Swap is active"):
+      # Doesn't matter if the numbers reported by `free` are slightly off due to unit conversions.
+      machine.succeed("free -h | grep -E 'Swap:\s+2[45][0-9]Mi'")
+  '';
+})