Erlang, eunit and gen_server: context cleanup failed

Question

I wrote some eunit test on my gen_server:

-module(st_db_tests).
-include_lib("eunit/include/eunit.hrl").

main_test_() ->
    {foreach,
     fun setup/0,
     fun cleanup/1,
     [
      fun db_server_up/1
     ]}.

setup() -> 
    {ok,Pid} = st_db:start_link(), Pid.
cleanup(Pid) -> 
    gen_server:call(Pid, stop).

db_server_up(Pid) ->    
    ?_assertMatch({[{<<"couchdb">>,<<"Welcome">>},{<<"version">>, _}]},
                  gen_server:call(Pid, test)).

When I make the test I have this:

./rebar eunit suite=st_db_tests skip_deps=true
==> site_stater (eunit)
Compiled test/st_db_tests.erl

... loading stuff ...

=PROGRESS REPORT==== 27-Jun-2011::12:33:21 ===
          supervisor: {local,kernel_safe_sup}
             started: [{pid,<0.127.0>},
                       {name,inet_gethost_native_sup},
                       {mfargs,{inet_gethost_native,start_link,[]}},
                       {restart_type,temporary},
                       {shutdown,1000},
                       {child_type,worker}]
module 'st_db_tests'
*** context cleanup failed ***
::exit:{normal,{gen_server,call,[<0.99.0>,stop]}}
  in function gen_server:call/2


=======================================================
  Failed: 0.  Skipped: 0.  Passed: 1.

Seems like the test has passed, but there is en error in context cleanup, which is not right, right?)

How can I fix this?

PS: my gen_server

-module(st_db).

-behaviour(gen_server).
%% --------------------------------------------------------------------
%% Include files
%% --------------------------------------------------------------------

%% --------------------------------------------------------------------
%% External exports
-export([start_link/0]).

%% gen_server callbacks
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).

-record(state, {db_pid, couch_server_pid}).

%% ====================================================================
%% External functions
%% ====================================================================

%%--------------------------------------------------------------------
%% @doc Starts the server.
%%
%% @spec start_link() -> {ok, Pid}
%% where
%%  Pid = pid()
%% @end
%%--------------------------------------------------------------------
start_link() ->
    gen_server:start_link({global, st_db}, ?MODULE, ["localhost", 5984, "site_stater"], []).

%% ====================================================================
%% Server internal functions
%% ====================================================================

%% --------------------------------------------------------------------
%% Function: init/1
%% Description: Initiates the server
%% Returns: {ok, State}          |
%%          {ok, State, Timeout} |
%%          ignore               |
%%          {stop, Reason}
%% --------------------------------------------------------------------
init([Server, Port, DB]) ->
    couchbeam:start(),
    CouchServer = couchbeam:server_connection(Server, Port, "", []),
    {ok, CouchDB} = couchbeam:open_or_create_db(CouchServer, DB, []),
    {ok, #state{db_pid=CouchDB, couch_server_pid=CouchServer}}.


%% ====================================================================
%% DB manipulation functions
%% ====================================================================


%% --------------------------------------------------------------------
%% Function: handle_call/3
%% Description: Handling call messages
%% Returns: {reply, Reply, State}          |
%%          {reply, Reply, State, Timeout} |
%%          {noreply, State}               |
%%          {noreply, State, Timeout}      |
%%          {stop, Reason, Reply, State}   | (terminate/2 is called)
%%          {stop, Reason, State}            (terminate/2 is called)
%% --------------------------------------------------------------------
handle_call (test, _From, #state{couch_server_pid = Couch_server_pid} = State) ->
    {ok, Version} = couchbeam:server_info(Couch_server_pid),
    {reply, Version, State};


handle_call(stop, _From, State) -> 
    {stop, normal, State}.

%% --------------------------------------------------------------------
%% Function: handle_cast/2
%% Description: Handling cast messages
%% Returns: {noreply, State}          |
%%          {noreply, State, Timeout} |
%%          {stop, Reason, State}            (terminate/2 is called)
%% --------------------------------------------------------------------

handle_cast(_Msg, State) ->
    {noreply, State}.

%% --------------------------------------------------------------------
%% Function: handle_info/2
%% Description: Handling all non call/cast messages
%% Returns: {noreply, State}          |
%%          {noreply, State, Timeout} |
%%          {stop, Reason, State}            (terminate/2 is called)
%% --------------------------------------------------------------------
handle_info(_Info, State) ->
    {noreply, State}.

%% --------------------------------------------------------------------
%% Function: terminate/2
%% Description: Shutdown the server
%% Returns: any (ignored by gen_server)
%% --------------------------------------------------------------------
terminate(_Reason, _State) ->
    ok.

%% --------------------------------------------------------------------
%% Func: code_change/3
%% Purpose: Convert process state when code is changed
%% Returns: {ok, NewState}
%% --------------------------------------------------------------------
code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

Answer 1

In the handle_call/2 function, you're returning:

{stop, normal, State}

rather than something like:

{stop, normal, ok, State}

In other words, you're not replying to the call. The client then see the server terminating (with normal reason) and it cries.

Didn't try it, but this would be my first guess.

Answer 2

It could be that the test finishes before the gen_server process has time to shut down. The gen_server is linked to the test process (because it is started with gen_server:start_link/4) and when the test finishes, the process is still running and is killed by EUnit.

Even if you return ok using {stop, normal, ok, State} as suggested by Roberto, the gen_server might be slower executing terminate/2 than the test takes clean up.

I usually use such a function in my tests or teardowns to wait for processes:

wait_for_exit(Pid) ->
    MRef = erlang:monitor(process, Pid),
    receive {'DOWN', MRef, _, _, _} -> ok end.

EUnit has a default timeout of 5000 ms that will be triggered if this function blocks for too long time.