add test to make sure duplocate headers issue is fixed

rebar.config

@@ -34,6 +34,6 @@
                            {top_level_readme,
                             {"./README.md", "http://github.com/benoitc/hackney"}}]}]},
              {test, [
-               {deps, [{cowboy, "1.0.4"}]}
+               {deps, [{cowboy, "1.0.4"}, {jsone, "1.4.3"}]}
              ]}
            ]}.

test/hackney_integration_tests.erl

@@ -17,13 +17,15 @@ all_tests() ->
    absolute_redirect_request_follow(),
    relative_redirect_request_no_follow(),
    relative_redirect_request_follow(),
+   test_duplicate_headers(),
    async_request(),
    async_head_request(),
    async_no_content_request()].
 
 %%all_tests() ->
 %%    case has_unix_socket() of
-%%        true -> default_tests() ++ [local_socket_request()];
+%%        true -> def
+%% ault_tests() ++ [local_socket_request()];
 %%        false -> default_tests()
 %%    end.
 
@@ -150,6 +152,18 @@ async_no_content_request() ->
     [?_assertEqual(204, StatusCode),
      ?_assertEqual([headers, status], Keys)].
 
+test_duplicate_headers() ->
+  URL = <<"http://localhost:8000/post">>,
+  Headers = [{<<"Content-Type">>, <<"application/json">>}],
+  Body = <<"{\"test\": \"ok\" }">>,
+  Options = [with_body],
+  {ok, 200, _H, JsonBody} = hackney:post(URL, Headers, Body, Options),
+  Obj = jsone:decode(JsonBody, [{object_format, proplist}]),
+  ReqHeaders = proplists:get_value(<<"headers">>, Obj),
+  ?_assertEqual(<<"application/json">>, proplists:get_value(<<"Content-Type">>, ReqHeaders)).
+
+
+
 %%local_socket_request() ->
 %%    URL = <<"http+unix://httpbin.sock/get">>,
 %%    {ok, StatusCode, _, _} = hackney:request(get, URL, [], <<>>, []),