The EUnit user guide is the best place to learn how to write tests. Of note is that all functions ending with _test or _test_ will be picked up as EUnit test cases.

Erlang.mk will automatically pick up tests found in any of the Erlang modules of your application. It will also pick up tests located in the $(TEST_DIR) directory, which defaults to test/.

It is generally a good practice to hide test code from the code you ship to production. With Erlang.mk, you can do this thanks to the TEST macro. It is only defined when running tests:

-ifdef(TEST).

%% Insert tests here.

-endif.

Be careful, however, if you include the EUnit header file, as it also defines the TEST macro. Make sure to only include it inside an ifdef block, otherwise tests will always be compiled.

-ifdef(TEST).

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

%% Insert tests here.

-endif.

Erlang.mk will automatically recompile your code when you perform a normal build after running tests, and vice versa.

The EUNIT_OPTS variable allows you to specify additional EUnit options. Options are documented in the EUnit manual. At the time of writing, the only available option is verbose:

EUNIT_OPTS = verbose

The EUNIT_ERL_OPTS variable allows you to specify options to be passed to erl when running EUnit tests. For example, you can load the vm.args and sys.config files:

EUNIT_ERL_OPTS = -args_file config/vm.args -config config/sys.config

To run all tests (including EUnit):

$ make tests

To run all tests and static checks (including EUnit):

$ make check

You can also run EUnit separately:

$ make eunit

EUnit will be quiet by default, only outputting errors. You can easily make it verbose for a single invocation:

$ make eunit EUNIT_OPTS=verbose

Erlang.mk allows you to run all tests from a specific module, or a specific test case from that module, using the variable t.

For example, to run all tests from the cow_http_hd module (instead of all tests from the entire project), one could write:

$ make eunit t=cow_http_hd

Similarly, to run a specific test case:

$ make eunit t=cow_http_hd:parse_accept_test_

To do the same against a multi-application repository, you can use the -C option:

$ make -C apps/my_app eunit t=my_module:hello_test

Note that this also applies to dependencies. From Cowboy, you can run the following directly:

$ make -C deps/cowlib eunit t=cow_http_hd

Finally, code coverage is available, but covered in its own chapter.