diff --git a/src/emqx.erl b/src/emqx.erl
index c39dde931..54f1952f4 100644
--- a/src/emqx.erl
+++ b/src/emqx.erl
@@ -94,8 +94,11 @@ unsubscribe(Topic) ->
     emqx_broker:unsubscribe(iolist_to_binary(Topic)).
 
 -spec(unsubscribe(topic() | string(), subscriber() | string()) -> ok | {error, term()}).
-unsubscribe(Topic, Subscriber) ->
-    emqx_broker:unsubscribe(iolist_to_binary(Topic), list_to_subid(Subscriber)).
+unsubscribe(Topic, Sub) when is_list(Sub) ->
+    emqx_broker:unsubscribe(iolist_to_binary(Topic));
+unsubscribe(Topic, Subscriber) when is_tuple(Subscriber) ->
+    {SubPid, SubId} = Subscriber,
+    emqx_broker:unsubscribe(iolist_to_binary(Topic), SubPid, SubId).
 
 %%--------------------------------------------------------------------
 %% PubSub management API
@@ -116,9 +119,9 @@ topics() -> emqx_router:topics().
 subscribers(Topic) ->
     emqx_broker:subscribers(iolist_to_binary(Topic)).
 
--spec(subscriptions(subscriber() | string()) -> [{topic(), subopts()}]).
+-spec(subscriptions(subscriber()) -> [{topic(), subopts()}]).
 subscriptions(Subscriber) ->
-    emqx_broker:subscriptions(list_to_subid(Subscriber)).
+    emqx_broker:subscriptions(Subscriber).
 
 -spec(subscribed(topic() | string(), subscriber()) -> boolean()).
 subscribed(Topic, Subscriber) ->
diff --git a/src/emqx_broker.erl b/src/emqx_broker.erl
index 8fed40b7f..560c095cf 100644
--- a/src/emqx_broker.erl
+++ b/src/emqx_broker.erl
@@ -379,9 +379,18 @@ code_change(_OldVsn, State, _Extra) ->
 %% Internal functions
 %%------------------------------------------------------------------------------
 
+insert_subscriber(Group, Topic, Subscriber) ->
+    Subscribers = subscribers(Topic),
+    case lists:member(Subscriber, Subscribers) of
+        false ->
+            ets:insert(?SUBSCRIBER, {Topic, shared(Group, Subscriber)});
+        _ ->
+            ok
+    end.
+
 do_subscribe(Group, Topic, Subscriber, SubOpts) ->
     ets:insert(?SUBSCRIPTION, {Subscriber, shared(Group, Topic)}),
-    ets:insert(?SUBSCRIBER, {Topic, shared(Group, Subscriber)}),
+    insert_subscriber(Group, Topic, Subscriber),
     ets:insert(?SUBOPTION, {{Topic, Subscriber}, SubOpts}).
 
 do_unsubscribe(Group, Topic, Subscriber) ->
diff --git a/test/emqx_mock_client.erl b/test/emqx_mock_client.erl
index 2b18c348f..e76e5551c 100644
--- a/test/emqx_mock_client.erl
+++ b/test/emqx_mock_client.erl
@@ -18,28 +18,42 @@
 
 -behaviour(gen_server).
 
--export([start_link/1, start_session/1, stop/1]).
+-export([start_link/1, open_session/3, stop/1]).
 
 -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
          terminate/2, code_change/3]).
 
--record(state, {clientid, session}).
+-record(state, {clean_start, client_id, client_pid}).
 
 start_link(ClientId) ->
     gen_server:start_link(?MODULE, [ClientId], []).
 
-start_session(CPid) ->
-    gen_server:call(CPid, start_session).
+open_session(ClientPid, ClientId, Zone) ->
+    gen_server:call(ClientPid, {start_session, ClientPid, ClientId, Zone}).
 
 stop(CPid) ->
     gen_server:call(CPid, stop).
 
 init([ClientId]) ->
-    {ok, #state{clientid = ClientId}}.
+    {ok, 
+     #state{clean_start = true,
+            client_id = ClientId}
+    }.
 
-handle_call(start_session, _From, State = #state{clientid = ClientId}) ->
-    {ok, SessPid, _} = emqx_sm:start_session(true, {ClientId, undefined}),
-    {reply, {ok, SessPid}, State#state{session = SessPid}};
+handle_call({start_session, ClientPid, ClientId, Zone}, _From, State) ->
+    Attrs = #{ zone        => Zone,
+               client_id   => ClientId,
+               client_pid  => ClientPid,
+               clean_start => true,
+               username    => undefined,
+               conn_props  => undefined
+             },
+    {ok, SessPid} = emqx_sm:open_session(Attrs),
+    {reply, {ok, SessPid}, State#state{
+                             clean_start = true,
+                             client_id = ClientId, 
+                             client_pid = ClientPid
+                            }};
 
 handle_call(stop, _From, State) ->
     {stop, normal, ok, State};