nixosTests.signal-desktop: add test

nixos/tests/all-tests.nix

@@ -222,6 +222,7 @@ in
   rxe = handleTest ./rxe.nix {};
   samba = handleTest ./samba.nix {};
   sddm = handleTest ./sddm.nix {};
+  signal-desktop = handleTest ./signal-desktop.nix {};
   simple = handleTest ./simple.nix {};
   slim = handleTest ./slim.nix {};
   slurm = handleTest ./slurm.nix {};

nixos/tests/signal-desktop.nix

@@ -0,0 +1,37 @@
+import ./make-test.nix ({ pkgs, ...} :
+
+{
+  name = "signal-desktop";
+  meta = with pkgs.stdenv.lib.maintainers; {
+    maintainers = [ flokli ];
+  };
+
+  machine = { ... }:
+
+  {
+    imports = [
+      ./common/user-account.nix
+      ./common/x11.nix
+    ];
+
+    services.xserver.enable = true;
+    services.xserver.displayManager.auto.user = "alice";
+    environment.systemPackages = [ pkgs.signal-desktop ];
+  };
+
+  enableOCR = true;
+
+  testScript = { nodes, ... }: let
+    user = nodes.machine.config.users.users.alice;
+  in ''
+    startAll;
+    $machine->waitForX;
+
+    # start signal desktop
+    $machine->execute("su - alice -c signal-desktop &");
+
+    # wait for the "Link your phone to Signal Desktop" message
+    $machine->waitForText(qr/Link your phone to Signal Desktop/);
+    $machine->screenshot("signal_desktop");
+  '';
+})