Add bare minimum test case

test/xdg_status_notifier_item_test.dart

@@ -1 +1,60 @@
-void main() {}
+import 'dart:io';
+
+import 'package:dbus/dbus.dart';
+import 'package:xdg_status_notifier_item/xdg_status_notifier_item.dart';
+import 'package:test/test.dart';
+
+class MockNotifierWatcherObject extends DBusObject {
+  MockNotifierWatcherObject() : super(DBusObjectPath('/StatusNotifierWatcher'));
+
+  @override
+  Future<DBusMethodResponse> handleMethodCall(DBusMethodCall methodCall) async {
+    if (methodCall.interface != 'org.kde.StatusNotifierWatcher') {
+      return DBusMethodErrorResponse.unknownInterface();
+    }
+
+    switch (methodCall.name) {
+      case 'RegisterStatusNotifierItem':
+        return DBusMethodSuccessResponse();
+
+      default:
+        return DBusMethodErrorResponse.unknownMethod();
+    }
+  }
+}
+
+class MockNotifierWatcherServer extends DBusClient {
+  late final MockNotifierWatcherObject _root;
+
+  MockNotifierWatcherServer(DBusAddress clientAddress) : super(clientAddress) {
+    _root = MockNotifierWatcherObject();
+  }
+
+  Future<void> start() async {
+    await requestName('org.kde.StatusNotifierWatcher');
+    await registerObject(_root);
+  }
+}
+
+void main() {
+  test('connect', () async {
+    var server = DBusServer();
+    var clientAddress =
+        await server.listenAddress(DBusAddress.unix(dir: Directory.systemTemp));
+    addTearDown(() async {
+      await server.close();
+    });
+
+    var watcher = MockNotifierWatcherServer(clientAddress);
+    await watcher.start();
+    addTearDown(() async {
+      await watcher.close();
+    });
+
+    var client = StatusNotifierItemClient(id: 'test', menu: DBusMenuItem());
+    addTearDown(() async {
+      await client.close();
+    });
+    await client.connect();
+  });
+}