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%%% Basic sequential statem based tests for dispcount.
-export([command/1, initial_state/0, next_state/3, postcondition/3,
-define(SERVER, dispcount).
-define(NAME, prop_dispatch).
-define(INFO, {call, erlang, element, [2,{call, dispcount, dispatcher_info, [?NAME]}]}).
-record(state, {resource=[], last}).
initial_state() ->
%% Checking in and checking out is always valid
command(#state{resource=R}) ->
oneof([{call, ?SERVER, checkout, [?INFO]}] ++
[{call, ?MODULE, checkin, [?INFO, hd(R)]} || R =/= []]).
next_state(S=#state{resource=L}, V, {call, _, checkout, _}) ->
S#state{resource=[V|L], last=checkout};
next_state(S=#state{resource=[_|L]}, _V, {call, _, checkin, _}) ->
S#state{resource=L, last=checkin}.
%% when we have a resource checked in or out, we can either try to
%% check it in or out again
precondition(#state{resource=R}, {call,_,checkin,_}) when R =/= [] -> true;
precondition(#state{resource=R}, {call,_,checkout,_}) when R =/= [] -> true;
%% Without a resource, we can only check stuff out.
precondition(#state{resource=[]}, {call,_,checkout,_}) -> true;
precondition(_, _) -> false.
%% The postconditions are a little bit more complex.
%% The following rules are for resources that we managed to check out.
postcondition(#state{resource=[{ok,_Ref,_Res}|_]}, {call, _, checkin, _}, ok) -> true;
postcondition(#state{resource=[{ok,_Ref,_Res}|_]}, {call, _, checkout, _}, {error,busy}) -> true;
%% These postconditions check for what happens when we were busy beforehand
%% This state pretty much allows anything to go
postcondition(#state{resource=[{error,busy}|_]}, {call, _, checkout, _}, {error,busy}) -> true;
postcondition(#state{resource=[{error,busy}|_]}, {call, _, checkin, _}, busy_checkin) -> true;
%% Checking out is always fine when we had no resource checked out beforehand
postcondition(#state{resource=[]}, {call, _, checkout, _}, {ok,_Ref,_Res}) -> true;
%% In case of a fast checkin following checkout on a similar resource might end up busy.
postcondition(#state{resource=[],last=checkin}, {call, _, checkout, _}, {error,busy}) -> true;
%% Gotta make sure we didn't manage to checkout the same resource twice
postcondition(#state{resource=L=[_|_]}, {call, _, checkout, _}, {ok,_Ref,Res}) ->
case lists:keyfind(Res,3,L) of
false -> true;
{ok,_,Res} -> false
postcondition(_, _, _) -> false.
prop_nocrash() ->
?FORALL(Cmds, commands(?MODULE, #state{}),
%% the ETS table works with the dispcount dispatcher
%% in this test to assign increasing IDs to each dispatch_watcher
%% instance.
Tid = ets:new(ids, [public,set]),
ets:insert(Tid, {id,0}),
ok = ?SERVER:start_dispatch(?NAME,
{?NAME, [Tid]},
{H,S,R} = run_commands(?MODULE, Cmds),
?WHENFAIL(io:format("History: ~p~n",[{Cmds,H}]),
R =:= ok))
%% Simple wrapper to work around limitations of statem stuff.
%% busy_checkin is basically a hack to circumvent the idea that the
%% previous result was a busy thing and we discard it through this function
checkin(_Info, {error,busy}) -> busy_checkin;
%% unpack & call the right checkin
checkin(Info, {ok, Ref, Res}) -> ?SERVER:checkin(Info, Ref, Res).
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