Add eunit cases and fix typo.

src/emqx_protocol.erl

@@ -71,6 +71,8 @@
 -compile(export_all).
 -endif.
 
+-define(NO_PROPS, undefined).
+
 -define(LOG(Level, Format, Args, PState),
         emqx_logger:Level([{client, PState#pstate.client_id}], "MQTT(~s@~s): " ++ Format,
                           [PState#pstate.client_id, esockd_net:format(PState#pstate.peername) | Args])).
@@ -672,7 +674,7 @@ authenticate(Credentials, Password) ->
             {error, Error}
     end.
 
-set_property(Name, Value, undefined) ->
+set_property(Name, Value, ?NO_PROPS) ->
     #{Name => Value};
 set_property(Name, Value, Props) ->
     Props#{Name => Value}.

test/emqx_protocol_tests.erl

@@ -0,0 +1,30 @@
+%% Copyright (c) 2018 EMQ Technologies Co., Ltd. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+
+-module(emqx_protocol_tests).
+
+-include_lib("eunit/include/eunit.hrl").
+
+set_property_test() ->
+    ?assertEqual(#{test => test_property}, emqx_protocol:set_property(test, test_property, undefined)),
+    TestMap = #{test => test_property},
+    ?assertEqual(#{test => test_property, test1 => test_property2},
+                 emqx_protocol:set_property(test1, test_property2, TestMap)),
+    ok.
+
+init_username_test() ->
+    ?assertEqual(<<"Peercert">>,
+                 emqx_protocol:init_username(<<"Peercert">>, [{peer_cert_as_username, crt}])),
+    ?assertEqual(undefined,
+                 emqx_protocol:init_username(undefined, [{peer_cert_as_username, undefined}])).