mopidy: restart service on config changes

Also extend basic configuration test a bit to verify the restart
trigger.

modules/services/mopidy.nix

@@ -126,6 +126,8 @@ in {
         Description = "mopidy music player daemon";
         Documentation = [ "https://mopidy.com/" ];
         After = [ "network.target" "sound.target" ];
+        X-Restart-Triggers = mkIf (cfg.settings != { })
+          [ "${config.xdg.configFile."mopidy/mopidy.conf".source}" ];
       };
 
       Service = {

tests/modules/services/mopidy/basic-configuration.nix

@@ -29,7 +29,28 @@
   };
 
   nmt.script = ''
-    assertFileExists home-files/.config/systemd/user/mopidy.service
+    serviceFile=home-files/.config/systemd/user/mopidy.service
+    assertFileExists $serviceFile
+    serviceFile=$(normalizeStorePaths $serviceFile)
+    assertFileContent $serviceFile \
+      ${
+        builtins.toFile "expected-mopidy.service" ''
+          [Install]
+          WantedBy=default.target
+
+          [Service]
+          ExecStart=/nix/store/00000000000000000000000000000000-mopidy-with-extensions/bin/mopidy --config /home/hm-user/.config/mopidy/mopidy.conf
+          Restart=on-failure
+
+          [Unit]
+          After=network.target
+          After=sound.target
+          Description=mopidy music player daemon
+          Documentation=https://mopidy.com/
+          X-Restart-Triggers=/nix/store/00000000000000000000000000000000-mopidy-hm-user
+        ''
+      }
+
     assertPathNotExists home-files/.config/systemd/user/mopidy-scan.service
 
     assertFileExists home-files/.config/mopidy/mopidy.conf