Testing a gen_server module using Common Test - erlang

Question

I have this (very simple) gen_server implementation:
-module(rand_gen).
-behaviour(gen_server).
-define(BASE, 1000).
%% Module Functionality
-export([start/0]).
-export([stop/1]).
-export([uniform/1, uniform/2]).
%% Callback Functions
-export([code_change/3]).
-export([init/1]).
-export([handle_call/3]).
-export([handle_cast/2]).
-export([handle_info/2]).
-export([terminate/2]).
%%%=======================================================================
%%% Export
%%%=======================================================================
-spec start() -> {ok, pid()} | {error, Reason :: term()}.
start() ->
gen_server:start(?MODULE, [], []).
-spec stop(Pid) -> ok when Pid :: pid().
stop(Pid) ->
gen_server:stop(Pid).
-spec uniform(Pid, Max) -> number() when Pid :: pid(), Max :: non_neg_integer().
uniform(Pid, Max) ->
gen_server:call(Pid, {uniform, #{max => Max}}).
-spec uniform(Pid) -> number() when Pid :: pid().
uniform(Pid) ->
gen_server:call(Pid, uniform).
%%%=======================================================================
%%% Callback Functions
%%%=======================================================================
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
handle_call({uniform, Input = #{max := Max}}, _From, _State) ->
{reply, rand:uniform(Max), Input};
handle_call(uniform, _From, State = #{max := Max}) ->
{reply, rand:uniform(Max), State};
handle_call(Msg, From, State) ->
io:format("Unexpected call [~p] from [~p]~n", [Msg, From]),
{reply, {error, no_call, Msg}, State}.
handle_cast(Msg, State) ->
io:format("Unexpected cast [~p]~n", [Msg]),
{noreply, State}.
handle_info(Msg, State) ->
io:format("Unexpected message ~p~n", [Msg]),
{noreply, State}.
init([]) ->
io:format("Crypto strong seed initialized! Using [~p] as base value.~n", [?BASE]),
<<I1:32/unsigned-integer, I2:32/unsigned-integer, I3:32/unsigned-integer>> = crypto:strong_rand_bytes(?BASE),
_ = rand:seed(exsplus, {I1, I2, I3}),
{ok, #{max => ?BASE}}.
terminate(_Reason, _StateData) ->
ok.
%%%=======================================================================
%%% Internal
%%%=======================================================================
Now I want to write a Common Test suite for testing it ‒ I just started learning this.
-module(rand_gen_SUITE).
-include_lib("common_test/include/ct.hrl").
-compile(export_all).
%%%=======================================================================
%%% Setup
%%%=======================================================================
all() ->
[
{group, generate}
].
groups() ->
[
{generate,
%%[parallel, {repeat, 3}],
[uniform]
}
].
init_per_suite(Config) ->
{ok, Pid} = rand_gen:start(),
[{pid, Pid} | Config].
end_per_suite(_Config) ->
ok.
%%%=======================================================================
%%% Test Cases
%%%=======================================================================
uniform(Config) ->
Pid = ?config(pid, Config),
true = is_number(rand_gen:uniform(Pid)).
...but every time I run the (super-small) suite/file I get back a weird message saying:
===> Running Common Test suites...
%%% rand_gen_SUITE ==> init_per_suite: FAILED
%%% rand_gen_SUITE ==> {{badmatch,<<3,217,51,126,122,17,213,209,222,82,29,106,213,128,218,98,129,12,
123,22,27,194,123,120,74,110,1,254,132,243,147,87,181,74,43,159,
163,94,58,224,18,40,46,190,134,198,43,225,57,81,109,216,64,245,
103,131,46,47,234,165,210,2,78,97,52,44,131,49,0,94,168,207,176,
214,38,69,235,105,116,240,92,37,112,17,16,47,86,0,179,4,167,61,
61,167,88,84,227,247,74,132,86,64,33,92,175,51,130,242,155,174,
167,126,142,100,123,35,77,159,198,113,105,182,43,61,130,173,169,
155,135,0,6,19,90,65,139,70,236,217,253,76,223,86,228,175,145,
198,89,40,251,158,6,193,177,66,202,199,110,39,130,232,28,37,176,
215,45,251,65,220,229,124,204,99,126,132,119,41,83,226,235,117,
152,69,179,211,10,97,194,128,147,134,26,240,175,218,188,204,82,
55,34,35,49,195,183,78,150,125,137,141,76,92,253,1,46,203,37,142,
224,236,8,252,94,129,89,108,84,133,88,213,56,127,255,48,172,26,
246,51,29,79,56,33,59,122,135,80,137,63,37,124,168,90,76,46,12,
155,241,182,16,218,147,227,16,110,9,51,213,74,216,18,51,219,12,
111,229,159,231,33,12,87,114,134,113,79,147,35,122,227,114,154,
52,164,223,95,66,162,136,231,174,47,93,10,66,62,63,76,196,232,
100,240,49,16,122,81,200,222,66,180,212,16,185,117,31,111,152,
216,10,125,212,138,203,219,31,67,94,170,181,160,225,189,182,10,
110,207,197,177,198,199,83,227,121,235,12,186,90,212,160,102,187,
99,61,127,123,255,76,36,63,190,197,175,167,175,132,230,187,162,
68,183,220,9,198,29,18,191,199,182,10,227,139,38,25,113,153,199,
80,244,13,55,62,153,250,165,218,137,211,210,129,123,35,67,226,20,
153,85,25,193,46,53,40,49,134,67,92,198,106,151,195,242,46,153,
223,187,163,100,205,108,253,191,192,220,65,101,15,32,161,41,25,
148,203,153,134,55,33,88,107,222,49,120,44,173,167,82,238,185,
213,107,164,45,64,28,180,253,34,131,92,49,112,202,188,1,36,59,81,
223,0,200,93,34,253,3,214,240,211,51,135,43,70,105,98,125,186,
131,129,85,246,147,167,238,32,176,54,92,250,200,73,63,246,72,159,
64,105,119,246,58,5,153,54,126,4,33,82,153,245,79,163,187,61,45,
172,173,30,45,148,252,230,74,80,213,132,45,52,202,101,234,98,30,
68,18,117,175,231,41,153,243,243,132,184,98,234,72,134,140,229,
239,205,136,228,223,52,189,118,250,195,178,126,33,56,142,247,242,
235,160,129,75,221,73,21,148,139,110,194,87,127,147,9,71,25,111,
218,6,206,38,3,208,154,128,236,127,96,155,223,25,164,139,80,170,
82,230,130,118,88,198,254,109,249,252,146,143,6,108,134,49,29,
152,215,67,74,96,240,109,6,97,36,145,250,234,48,145,17,144,217,
198,236,60,68,213,30,7,120,228,117,41,231,72,208,245,73,153,251,
64,195,16,201,250,12,143,23,138,23,215,74,5,180,228,133,236,61,
227,123,188,100,81,77,254,187,69,213,127,22,38,143,84,184,4,47,
47,124,245,230,221,105,105,36,220,28,52,200,195,104,7,78,155,250,
36,8,42,228,166,212,106,147,247,101,21,230,78,236,91,217,115,84,
76,125,193,18,136,103,85,104,33,102,7,235,250,197,139,238,187,
154,12,84,152,174,133,92,165,72,76,45,70,90,115,32,161,156,251,
197,103,70,141,168,220,223,251,252,14,249,172,40,122,53,69,137,
45,29,129,144,146,238,181,104,28,117,166,19,238,44,162,174,117,
250,21,62,155,39,149,221,207,48,168,19,35,209,53,188,31,122,99,
83,74,138,164,103,72,106,27,175,239,240,3,100,118,152,180,225,82,
227,60,108,66,223,165,173,183,46,166,23,85,236,141,238,166,160,
114,31,7,14,23,220,90,226,79,217,203,240,126,128,241,41,149,224,
148,130,86,130,244,12,27,237,123,234,0,68,164,165,250,235,87,243,
217,253,215,249,13,206,155,197,138,192,249,154,104,131,109,229,
126,77,216,127,254,55,170,192,100,90,49,30,78,209,249,140,184,81,
121,164,178,50,204,131,144,214,8,12,130,32,164,149,92,200,235,
145,48,162,244,238,114,47,251,31,79,242,186,111,117,207,16,178,
212,234,209,161,143,21,241,111,218,32,255,191,70,177,203,5,117,
182,148,199,231,93,118,76,72>>},
[{rand_gen,init,1,
[{file,"/home/x80486/Workshop/erlang/erlang_basics/_build/test/lib/erlang_basics/src/rand_gen.erl"},
{line,74}]},
{rand_gen_SUITE,init_per_suite,1,
[{file,"/home/x80486/Workshop/erlang/erlang_basics/_build/test/lib/erlang_basics/test/rand_gen_SUITE.erl"},
{line,34}]},
{test_server,ts_tc,3,[{file,"test_server.erl"},{line,1546}]},
{test_server,run_test_case_eval1,6,[{file,"test_server.erl"},{line,1147}]},
{test_server,run_test_case_eval,9,[{file,"test_server.erl"},{line,994}]}]}
Any clues? Thanks in advance!

Answer 1

That’s because the result of crypto:strong_rand_bytes(?BASE) doesn’t match <<I1:32/unsigned-integer, I2:32/unsigned-integer, I3:32/unsigned-integer>> since it’s (as you can see in the error) longer than that.
You can try changing that line in your code to something like:
<<I1:32/unsigned-integer, I2:32/unsigned-integer, I3:32/unsigned-integer, _/bitstring>> = crypto:strong_rand_bytes(?BASE),