nixos/test/systemd-localed: services.xserver.xkb.layout should be respected

nixos/tests/all-tests.nix

@@ -1684,6 +1684,7 @@ in
   systemd-journal = runTest ./systemd-journal.nix;
   systemd-journal-gateway = runTest ./systemd-journal-gateway.nix;
   systemd-journal-upload = runTest ./systemd-journal-upload.nix;
+  systemd-localed = runTest ./systemd-localed.nix;
   systemd-lock-handler = runTestOn [ "aarch64-linux" "x86_64-linux" ] ./systemd-lock-handler.nix;
   systemd-machinectl = runTest ./systemd-machinectl.nix;
   systemd-misc = runTest ./systemd-misc.nix;

nixos/tests/systemd-localed.nix

@@ -0,0 +1,23 @@
+{ lib, ... }:
+{
+  name = "systemd-localed";
+  meta.maintainers = [ lib.maintainers.haansn08 ];
+
+  nodes.machine = { ... }: {
+    # we don't use services.xserver.enable because some window managers like
+    # niri rely on systemd-localed for the keyboard layout:
+    # https://niri-wm.github.io/niri/Configuration%3A-Input.html#layout
+    services.graphical-desktop.enable = true;
+
+    services.xserver.xkb.layout = "jp";
+  };
+
+  testScript = ''
+    machine.start()
+    machine.wait_for_unit("default.target")
+    machine.wait_for_unit("dbus.socket")
+
+    status, stdout = machine.execute("localectl")
+    t.assertIn("X11 Layout: jp", stdout)
+  '';
+}