[[coverage]]
== Code coverage

Erlang.mk provides support for code coverage via the tool
`cover` that comes with Erlang/OTP. Code coverage lets you
see what parts of your code are covered by the tests.

=== Enabling cover when running tests

To run tests with code coverage enabled, simply define
`COVER=1` either on the command line or in your Makefile:

[source,bash]
$ make tests COVER=1

When running the targets `tests` or `check` the code
coverage report will be built automatically. This is
not the case for test framework specific targets,
however. In those cases you can generate the reports
manually:

[source,bash]
$ make eunit proper COVER=1
$ make cover-report

Note that Common Test has some support for `cover`
built-in and that it will generate code coverage
reports in the Common Test logs regardless. The
report that Erlang.mk generates is however common
to all test frameworks and might be more useful.

=== Adding applications to the cover report

By default Erlang.mk will include all the applications
in the code coverage report, except external dependencies.

To include some dependencies in the report, you can
define the `COVER_DEPS` variable:

[source,make]
COVER_DEPS = cowlib

When using multi application repositories you can exclude
some applications by defining the `COVER_APPS` variable:

[source,make]
COVER_APPS = presence backend

=== Removing modules from the cover report

By default Erlang.mk will include all modules in the
cover report.

To exclude some modules from the report, you can
define the `COVER_EXCLUDE_MODS` variable:

[source,make]
COVER_EXCLUDE_MODS = cowboy_app cowboy_sup

=== Configuring paths

By default Erlang.mk will store 'coverdata' files and
code coverage reports under the 'cover/' directory. The
variables `COVER_DATA_DIR` and `COVER_REPORT_DIR` can be
set to use a different location.

=== Merging coverdata files

The target `all.coverdata` will take all existing
'coverdata' files and merge them into one:

[source,bash]
$ make all.coverdata