Add gnome 3.12 test

nixos/tests/gnome3_12.nix

@@ -0,0 +1,30 @@
+import ./make-test.nix {
+
+  machine =
+    { config, pkgs, ... }:
+
+    { imports = [ ./common/user-account.nix ];
+
+      services.xserver.enable = true;
+
+      services.xserver.displayManager.auto.enable = true;
+      services.xserver.displayManager.auto.user = "alice";
+      services.xserver.desktopManager.gnome3.enable = true;
+      environment.gnome3.packageSet = pkgs.gnome3_12;
+    };
+
+  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(10);
+      $machine->screenshot("screen");
+    '';
+
+}