Documentation should explain how to use it instead of `eunit.hrl`

[rlipscombe]

Most projects don't include stdlib/include/assert.hrl; they include eunit/include/eunit.hrl. This is so that their _test and _test_ functions are automatically picked up by the parse transform.

How does one do the same with this library? I've tried a bunch of finagling the include file order and messing around with defines, and I'm not seeing the shiny new thing.

[robertoaloi]

Thanks for the report @rlipscombe !

I briefly checked the eunit code and it looks like the testing framework has its own mechanism to print the stacktrace, which does not respect the erl_error metadata. I also see OTP has a somewhat related issue about this.

In principle, a fix in eunit such as this, where eunit uses the erl_error module, should make it work:

print_test_error({error, {C, R, S} = Exception}, Data, #state{print_depth = Depth}) ->
    Output = proplists:get_value(output, Data),
    fwrite("*failed*\n~ts", [erl_error:format_exception(C, R, S)]),
    ...

As opposed to the current:

print_test_error({error, Exception}, Data, #state{print_depth = Depth}) ->
    Output = proplists:get_value(output, Data),
    fwrite("*failed*\n~ts", [eunit_lib:format_exception(Exception, Depth)]),
    ...

But it probably requires some attention from the OTP team.

[rlipscombe]

Interesting, but I hadn't even got that far yet (or have I and you're answering an implied question?).

My question is simply this: I've got -include_lib("eunit/include/eunit.hrl").. If I replace it with -include_lib("assert/include/assert.hrl")., then the eunit parse transform doesn't do its thing, so I don't have any tests.

If I include both (eunit.hrl first), then -- as far as I can tell -- I just get the eunit-style assertion failures (I had to disable unite first, obvs.). I'm using erlang.mk incidentally.

[robertoaloi]

What I am trying to say is that eunit seems to be currently incompatible with this library. On a test file, you should simply be able to enable the fancy diffs by simply replacing:

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

With:

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

But this currently does not work because EUnit has its own way to format the exception, instead of relying on the more standard erl_errror mechanism. This will need a EUnit patch to work.