Add test for emacs module

nixos/tests/emacs-daemon.nix

@@ -0,0 +1,45 @@
+import ./make-test.nix ({ pkgs, ...} : {
+  name = "emacs-daemon";
+  meta = with pkgs.stdenv.lib.maintainers; {
+    maintainers = [ DamienCassou ];
+  };
+
+  enableOCR = true;
+
+  machine =
+    { config, pkgs, ... }:
+
+    { imports = [ ./common/x11.nix ];
+      services.emacs = {
+        enable = true;
+        defaultEditor = true;
+      };
+
+      # Important to get the systemd service running for root
+      environment.variables.XDG_RUNTIME_DIR = "/run/user/0";
+
+      environment.variables.TEST_SYSTEM_VARIABLE = "system variable";
+    };
+
+  testScript =
+    ''
+      $machine->waitForUnit("multi-user.target");
+
+      # checks that the EDITOR environment variable is set
+      $machine->succeed("test \$(basename \"\$EDITOR\") = emacseditor");
+
+      # waits for the emacs service to be ready
+      $machine->waitUntilSucceeds("systemctl --user status emacs.service | grep 'Active: active'");
+
+      # connects to the daemon
+      $machine->succeed("emacsclient --create-frame \$EDITOR &");
+
+      # checks that Emacs shows the edited filename
+      $machine->waitForText("emacseditor");
+
+      # makes sure environment variables are accessible from Emacs
+      $machine->succeed("emacsclient --eval '(getenv \"TEST_SYSTEM_VARIABLE\")'") =~ /system variable/ or die;
+
+      $machine->screenshot("emacsclient");
+    '';
+})