add message_reaction_modal_test

test/src/mocks.dart

@@ -0,0 +1,10 @@
+import 'package:mockito/mockito.dart';
+import 'package:stream_chat/stream_chat.dart';
+
+class MockClient extends Mock implements Client {}
+
+class MockClientState extends Mock implements ClientState {}
+
+class MockChannel extends Mock implements Channel {}
+
+class MockChannelState extends Mock implements ChannelClientState {}