nixos/tests/gnome3-gdm: port to wayland

The test now runs wayland, which means we can no longer use X11 style testing.
Instead we get gnome shell to execute javascript through its dbus interface.

nixos/tests/gnome3-gdm.nix

@@ -23,22 +23,38 @@ import ./make-test.nix ({ pkgs, ...} : {
       virtualisation.memorySize = 1024;
     };
 
-  testScript =
-    ''
-      # wait for gdm to start and bring up X
+  testScript = let
+    # Keep line widths somewhat managable
+    bus = "DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus";
+    gdbus = "${bus} gdbus";
+    # Call javascript in gnome shell, returns a tuple (success, output), where
+    # `success` is true if the dbus call was successful and output is what the
+    # javascript evaluates to.
+    eval = "call --session -d org.gnome.Shell -o /org/gnome/Shell -m org.gnome.Shell.Eval";
+    # False when startup is done
+    startingUp = "${gdbus} ${eval} Main.layoutManager._startingUp";
+    # Hopefully gnome-terminal's wm class
+    wmClass = "${gdbus} ${eval} global.display.focus_window.wm_class";
+  in ''
+      # wait for gdm to start
       $machine->waitForUnit("display-manager.service");
-      $machine->waitForX;
 
       # wait for alice to be logged in
       $machine->waitForUnit("default.target","alice");
 
       # Check that logging in has given the user ownership of devices.
       $machine->succeed("getfacl /dev/snd/timer | grep -q alice");
 
-      # open a terminal and check it's there
-      $machine->succeed("su - alice -c 'DISPLAY=:0.0 XAUTHORITY=/run/user/\$UID/gdm/Xauthority gnome-terminal'");
-      $machine->succeed("xauth merge /run/user/1000/gdm/Xauthority");
-      $machine->waitForWindow(qr/Terminal/);
+      # Wait for the wayland server
+      $machine->waitForFile("/run/user/1000/wayland-0");
+
+      # Wait for gnome shell, correct output should be "(true, 'false')"
+      $machine->waitUntilSucceeds("su - alice -c '${startingUp} | grep -q true,..false'");
+
+      # open a terminal
+      $machine->succeed("su - alice -c '${bus} gnome-terminal'");
+      # and check it's there
+      $machine->waitUntilSucceeds("su - alice -c '${wmClass} | grep -q gnome-terminal-server'");
 
       # wait to get a nice screenshot
       $machine->sleep(20);