[erlang-questions] Ensuring a process is crashed with raise/3 in a Common_Test case

[Jared Davison]

Hi Edmond,

Thanks for your reply, it was very helpful.

I had something like:

    ?assertMatch({timeout,_},
        try
            gen_statem:call(foo, bar, 5000),
            timeout_was_not_thrown
        catch
            A -> A
        end).

Adding the exit class as you have suggested in the catch pattern match
seems to do the trick:

    ?assertMatch({timeout,_},
        try
            gen_statem:call(foo, bar, 5000),
            timeout_was_not_thrown
        catch
            exit:A -> A
        end).

Thanks again.

Jared

On Wed, Aug 15, 2018 at 10:40 PM, Edmond Begumisa <
ebegumisa@REDACTED> wrote:

> On Wed, 15 Aug 2018 14:17:40 +1000, Jared Davison <
> jared@REDACTED> wrote:
>
> Hi,
>>
>> Could you please assist me in using common test.
>>
>> I'm trying to ensure that a gen_statem:call/3 raises a {timeout, _} in a
>> common test case.
>>
>> At first I tried a catch because I thought it would be a throw but it
>> catches nothing.
>>
>
> Sounds like you're catching the wrong exception class. For gen_* timeouts,
> I believe the exception class is 'exit' rather than 'throw'.
>
>
> Digging into the gen_statem:call/3 code it appears that it uses
>> erlang:raise/3 which stops the >execution of the process, so that makes
>> sense that catch does nothing.
>>
>
> Catch should do something if you're catching the right exception class
> ('exit') or matching any exception class ('_'). It is still possible to
> catch exceptions generated using erlang:raise/3 for any class
> ('error'|'throw'|'exit'). E.g from an erlang shell ...
>
>     $ try erlang:raise(exit, foo, []) catch exit:foo -> yep end.
>
> ... returns 'yep'. As do...
>
>     $ try erlang:raise(throw, foo, []) catch throw:foo -> yep end.
>     $ try erlang:raise(error, foo, []) catch error:foo -> yep end.
>
> ... so do...
>
>     $ try exit(foo) catch exit:foo -> yep end.
>     $ try throw(foo) catch throw:foo -> yep end.
>     $ try error(foo) catch error:foo -> yep end.
>
> ... and also ...
>
>     $ try erlang:raise(exit, foo, []) catch _:foo -> yep end.
>     $ try erlang:raise(error, foo, []) catch _:foo -> yep end.
>     $ try erlang:raise(throw, foo, []) catch _:foo -> yep end.
>     $ try exit(foo) catch _:foo -> yep end.
>     $ try throw(foo) catch _:foo -> yep end.
>     $ try error(foo) catch _:foo -> yep end.
>
> I want to be sure that the process was stopped with the a particular
>> reason, and pass the test if >it does.
>> Is this possible in Common Test?
>>
>
> Should be. My guess is that your test case is catching something like so...
>
>     <snip>
>
>     try gen_statem:call(foo, bar, 5000)
>     catch throw:{timeout,_} -> ..
>     end.
>
>     </snip>
>
> Try changing that to...
>
>     <snip>
>
>     try gen_statem:call(foo, bar, 5000)
>     catch exit:{timeout,_} -> ..
>     end.
>
>     </snip>
>
> - Edmond -
>
>
>> Thanks
>>
>> Jared
>>
>>
>>
>>
>
>
> --
> Using Opera's mail client: http://www.opera.com/mail/
>
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