tests: add make-disk-image-zfs.nix

This uses the simple zfs on root example to test that zfs disk images
can be made in CI

Author: MatthewCroughan

tests/make-disk-image-zfs.nix

@@ -0,0 +1,26 @@
+{
+  pkgs ? import <nixpkgs> { },
+  ...
+}:
+
+(pkgs.nixos [
+  ../module.nix
+  ../example/zfs-simple-root.nix
+  (
+    { config, ... }:
+    {
+      networking.hostId = "00000000";
+
+      # Adds some weight to the closure size to test real world usage
+      disko.devices.disk.disk1.imageSize = "5G";
+      environment.systemPackages = with pkgs; [
+        chromium
+        firefox
+      ];
+
+      documentation.enable = false;
+      system.stateVersion = config.system.nixos.release;
+      disko.checkScripts = true;
+    }
+  )
+]).config.system.build.diskoImages