How to debug my Eunit test suite run when using rebar3?

Question

I have created an release app with rebar3 (beta-4). Added some eunit tests and wrote some code.

For now I have to debug one test case to see what I have to add to make the implementation to work properly.

I found some articles about using dbg from Erlang console and I found how to write debug info from Eunit. But I need to get info from code that I have to test (the actual implementation(logic)).

Is there a way to debug Erlang code (actual source code, not the test one) when rebar3 is used with eunit argument?

I'm using tracing in terminal like there: https://aloiroberto.wordpress.com/2009/02/23/tracing-erlang-functions/

Answer 1

One way to do this is use rebar3 to run a shell under the test profile, then start the debugger and set up your breakpoints and such:

$ rebar3 as test shell
...
1> debugger:start().
{ok, <0.67.0>}

This will pop up the debugger GUI. Once the debugger is set up and ready, run your test under eunit:

2> eunit:test(your_test_module,[verbose]).
======================== EUnit ========================
your_test_module: xyz_test_ (module 'your_test_module')...

Assuming you set up a suitable breakpoint in the debugger, this will hit it, but you'll likely run into a problem with this approach: by default, eunit tests time out after 5 seconds, which doesn't give you much time for debugging. You need to specify a longer timeout for your test, which is why the example above shows that what's running is a test fixture named xyz_test_, which wraps the actual test with a long timeout. Such a fixture is pretty simple:

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

xyz_test_() ->
    {timeout,3600,
     [fun() -> ?assertMatch(expected_value, my_module:my_fun()), ok end]}.

Here, the actual test is the anonymous function, which matches the return value from my_module:my_fun/0, which for this example represents the business logic under test. This example fixture sets the test timeout to one hour; you can of course set it as needed for your application.