[google_maps_flutter_android] Add tests for cluster manager utils

packages/google_maps_flutter/google_maps_flutter_android/test/cluster_manager_utils_test.dart

@@ -0,0 +1,59 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+import 'package:flutter_test/flutter_test.dart';
+import 'package:google_maps_flutter_android/src/utils/cluster_manager_utils.dart';
+import 'package:google_maps_flutter_platform_interface/google_maps_flutter_platform_interface.dart';
+
+void main() {
+  test('serializeClusterManagerUpdates', () async {
+    const ClusterManagerId clusterManagerId1 = ClusterManagerId('cm1');
+    const ClusterManagerId clusterManagerId2 = ClusterManagerId('cm2');
+
+    const ClusterManager clusterManager1 = ClusterManager(
+      clusterManagerId: clusterManagerId1,
+    );
+    const ClusterManager clusterManager2 = ClusterManager(
+      clusterManagerId: clusterManagerId2,
+    );
+
+    final Set<ClusterManager> clusterManagersSet1 = <ClusterManager>{};
+    final Set<ClusterManager> clusterManagersSet2 = <ClusterManager>{
+      clusterManager1,
+      clusterManager2
+    };
+    final Set<ClusterManager> clusterManagersSet3 = <ClusterManager>{
+      clusterManager1
+    };
+
+    final ClusterManagerUpdates clusterManagerUpdates1 =
+        ClusterManagerUpdates.from(clusterManagersSet1, clusterManagersSet2);
+    final Map<String, Object> serializedData1 =
+        serializeClusterManagerUpdates(clusterManagerUpdates1)
+            as Map<String, Object>;
+    expect(serializedData1['clusterManagersToAdd'], isNotNull);
+    final List<Object> clusterManagersToAdd1 =
+        serializedData1['clusterManagersToAdd']! as List<Object>;
+    expect(clusterManagersToAdd1.length, 2);
+    expect(serializedData1['clusterManagerIdsToRemove'], isNotNull);
+    final List<Object> clusterManagersToRemove1 =
+        serializedData1['clusterManagerIdsToRemove']! as List<Object>;
+    expect(clusterManagersToRemove1.length, 0);
+
+    final ClusterManagerUpdates clusterManagerUpdates2 =
+        ClusterManagerUpdates.from(clusterManagersSet2, clusterManagersSet3);
+    serializeClusterManagerUpdates(clusterManagerUpdates2);
+    final Map<String, Object> serializedData2 =
+        serializeClusterManagerUpdates(clusterManagerUpdates2)
+            as Map<String, Object>;
+    expect(serializedData2['clusterManagersToAdd'], isNotNull);
+    final List<Object> clusterManagersToAdd2 =
+        serializedData2['clusterManagersToAdd']! as List<Object>;
+    expect(clusterManagersToAdd2.length, 0);
+    expect(serializedData1['clusterManagerIdsToRemove'], isNotNull);
+    final List<Object> clusterManagersToRemove2 =
+        serializedData2['clusterManagerIdsToRemove']! as List<Object>;
+    expect(clusterManagersToRemove2.length, 1);
+    expect(clusterManagersToRemove2.first as String, equals('cm2'));
+  });
+}