nixos tests: add gdm test

nixos/release.nix

@@ -226,6 +226,7 @@ in rec {
   tests.fleet = hydraJob (import tests/fleet.nix { system = "x86_64-linux"; });
   #tests.gitlab = callTest tests/gitlab.nix {};
   tests.gnome3 = callTest tests/gnome3.nix {};
+  tests.gnome3-gdm = callTest tests/gnome3-gdm.nix {};
   tests.i3wm = callTest tests/i3wm.nix {};
   tests.installer.grub1 = forAllSystems (system: hydraJob (import tests/installer.nix { inherit system; }).grub1.test);
   tests.installer.lvm = forAllSystems (system: hydraJob (import tests/installer.nix { inherit system; }).lvm.test);

nixos/tests/gnome3-gdm.nix

@@ -0,0 +1,39 @@
+import ./make-test.nix ({ pkgs, ...} : {
+  name = "gnome3-gdm";
+  meta = with pkgs.stdenv.lib.maintainers; {
+    maintainers = [ lethalman ];
+  };
+
+  machine =
+    { config, pkgs, ... }:
+
+    { imports = [ ./common/user-account.nix ];
+
+      services.xserver.enable = true;
+
+      services.xserver.displayManager.gdm = {
+        enable = true;
+        autoLogin = {
+          enable = true;
+          user = "alice";
+        };
+      };
+      services.xserver.desktopManager.gnome3.enable = true;
+
+      virtualisation.memorySize = 512;
+    };
+
+  testScript =
+    ''
+      $machine->waitForX;
+      $machine->sleep(15);
+
+      # Check that logging in has given the user ownership of devices.
+      $machine->succeed("getfacl /dev/snd/timer | grep -q alice");
+
+      $machine->succeed("su - alice -c 'DISPLAY=:0.0 gnome-terminal &'");
+      $machine->waitForWindow(qr/Terminal/);
+      $machine->sleep(20);
+      $machine->screenshot("screen");
+    '';
+})