path: root/Documentation/dev-tools/kunit/running_tips.rst

.. SPDX-License-Identifier: GPL-2.0

============================
Tips For Running KUnit Tests
============================

Using ``kunit.py run`` ("kunit tool")
=====================================

Running from any directory
--------------------------

It can be handy to create a bash function like:

.. code-block:: bash

	function run_kunit() {
	  ( cd "$(git rev-parse --show-toplevel)" && ./tools/testing/kunit/kunit.py run $@ )
	}

.. note::
	Early versions of ``kunit.py`` (before 5.6) didn't work unless run from
	the kernel root, hence the use of a subshell and ``cd``.

Running a subset of tests
-------------------------

``kunit.py run`` accepts an optional glob argument to filter tests. Currently
this only matches against suite names, but this may change in the future.

Say that we wanted to run the sysctl tests, we could do so via:

.. code-block:: bash

	$ echo -e 'CONFIG_KUNIT=y\nCONFIG_KUNIT_ALL_TESTS=y' > .kunit/.kunitconfig
	$ ./tools/testing/kunit/kunit.py run 'sysctl*'

We're paying the cost of building more tests than we need this way, but it's
easier than fiddling with ``.kunitconfig`` files or commenting out
``kunit_suite``'s.

However, if we wanted to define a set of tests in a less ad hoc way, the next
tip is useful.

Defining a set of tests
-----------------------

``kunit.py run`` (along with ``build``, and ``config``) supports a
``--kunitconfig`` flag. So if you have a set of tests that you want to run on a
regular basis (especially if they have other dependencies), you can create a
specific ``.kunitconfig`` for them.

E.g. kunit has one for its tests:

.. code-block:: bash

	$ ./tools/testing/kunit/kunit.py run --kunitconfig=lib/kunit/.kunitconfig

Alternatively, if you're following the convention of naming your
file ``.kunitconfig``, you can just pass in the dir, e.g.

.. code-block:: bash

	$ ./tools/testing/kunit/kunit.py run --kunitconfig=lib/kunit

.. note::
	This is a relatively new feature (5.12+) so we don't have any
	conventions yet about on what files should be checked in versus just
	kept around locally. It's up to you and your maintainer to decide if a
	config is useful enough to submit (and therefore have to maintain).

.. note::
	Having ``.kunitconfig`` fragments in a parent and child directory is
	iffy. There's discussion about adding an "import" statement in these
	files to make it possible to have a top-level config run tests from all
	child directories. But that would mean ``.kunitconfig`` files are no
	longer just simple .config fragments.

	One alternative would be to have kunit tool recursively combine configs
	automagically, but tests could theoretically depend on incompatible
	options, so handling that would be tricky.

Generating code coverage reports under UML
------------------------------------------

.. note::
	TODO(brendanhiggins@google.com): There are various issues with UML and
	versions of gcc 7 and up. You're likely to run into missing ``.gcda``
	files or compile errors. We know one `faulty GCC commit
	<https://github.com/gcc-mirror/gcc/commit/8c9434c2f9358b8b8bad2c1990edf10a21645f9d>`_
	but not how we'd go about getting this fixed. The compile errors still
	need some investigation.

.. note::
	TODO(brendanhiggins@google.com): for recent versions of Linux
	(5.10-5.12, maybe earlier), there's a bug with gcov counters not being
	flushed in UML. This translates to very low (<1%) reported coverage. This is
	related to the above issue and can be worked around by replacing the
	one call to ``uml_abort()`` (it's in ``os_dump_core()``) with a plain
	``exit()``.


This is different from the "normal" way of getting coverage information that is
documented in Documentation/dev-tools/gcov.rst.

Instead of enabling ``CONFIG_GCOV_KERNEL=y``, we can set these options:

.. code-block:: none

	CONFIG_DEBUG_KERNEL=y
	CONFIG_DEBUG_INFO=y
	CONFIG_GCOV=y


Putting it together into a copy-pastable sequence of commands:

.. code-block:: bash

	# Append coverage options to the current config
	$ echo -e "CONFIG_DEBUG_KERNEL=y\nCONFIG_DEBUG_INFO=y\nCONFIG_GCOV=y" >> .kunit/.kunitconfig
	$ ./tools/testing/kunit/kunit.py run
	# Extract the coverage information from the build dir (.kunit/)
	$ lcov -t "my_kunit_tests" -o coverage.info -c -d .kunit/

	# From here on, it's the same process as with CONFIG_GCOV_KERNEL=y
	# E.g. can generate an HTML report in a tmp dir like so:
	$ genhtml -o /tmp/coverage_html coverage.info


If your installed version of gcc doesn't work, you can tweak the steps:

.. code-block:: bash

	$ ./tools/testing/kunit/kunit.py run --make_options=CC=/usr/bin/gcc-6
	$ lcov -t "my_kunit_tests" -o coverage.info -c -d .kunit/ --gcov-tool=/usr/bin/gcov-6


Running tests manually
======================

Running tests without using ``kunit.py run`` is also an important use case.
Currently it's your only option if you want to test on architectures other than
UML.

As running the tests under UML is fairly straightforward (configure and compile
the kernel, run the ``./linux`` binary), this section will focus on testing
non-UML architectures.


Running built-in tests
----------------------

When setting tests to ``=y``, the tests will run as part of boot and print
results to dmesg in TAP format. So you just need to add your tests to your
``.config``, build and boot your kernel as normal.

So if we compiled our kernel with:

.. code-block:: none

	CONFIG_KUNIT=y
	CONFIG_KUNIT_EXAMPLE_TEST=y

Then we'd see output like this in dmesg signaling the test ran and passed:

.. code-block:: none

	TAP version 14
	1..1
	    # Subtest: example
	    1..1
	    # example_simple_test: initializing
	    ok 1 - example_simple_test
	ok 1 - example

Running tests as modules
------------------------

Depending on the tests, you can build them as loadable modules.

For example, we'd change the config options from before to

.. code-block:: none

	CONFIG_KUNIT=y
	CONFIG_KUNIT_EXAMPLE_TEST=m

Then after booting into our kernel, we can run the test via

.. code-block:: none

	$ modprobe kunit-example-test

This will then cause it to print TAP output to stdout.

.. note::
	The ``modprobe`` will *not* have a non-zero exit code if any test
	failed (as of 5.13). But ``kunit.py parse`` would, see below.

.. note::
	You can set ``CONFIG_KUNIT=m`` as well, however, some features will not
	work and thus some tests might break. Ideally tests would specify they
	depend on ``KUNIT=y`` in their ``Kconfig``'s, but this is an edge case
	most test authors won't think about.
	As of 5.13, the only difference is that ``current->kunit_test`` will
	not exist.

Pretty-printing results
-----------------------

You can use ``kunit.py parse`` to parse dmesg for test output and print out
results in the same familiar format that ``kunit.py run`` does.

.. code-block:: bash

	$ ./tools/testing/kunit/kunit.py parse /var/log/dmesg


Retrieving per suite results
----------------------------

Regardless of how you're running your tests, you can enable
``CONFIG_KUNIT_DEBUGFS`` to expose per-suite TAP-formatted results:

.. code-block:: none

	CONFIG_KUNIT=y
	CONFIG_KUNIT_EXAMPLE_TEST=m
	CONFIG_KUNIT_DEBUGFS=y

The results for each suite will be exposed under
``/sys/kernel/debug/kunit/<suite>/results``.
So using our example config:

.. code-block:: bash

	$ modprobe kunit-example-test > /dev/null
	$ cat /sys/kernel/debug/kunit/example/results
	... <TAP output> ...

	# After removing the module, the corresponding files will go away
	$ modprobe -r kunit-example-test
	$ cat /sys/kernel/debug/kunit/example/results
	/sys/kernel/debug/kunit/example/results: No such file or directory

Generating code coverage reports
--------------------------------

See Documentation/dev-tools/gcov.rst for details on how to do this.

The only vaguely KUnit-specific advice here is that you probably want to build
your tests as modules. That way you can isolate the coverage from tests from
other code executed during boot, e.g.

.. code-block:: bash

	# Reset coverage counters before running the test.
	$ echo 0 > /sys/kernel/debug/gcov/reset
	$ modprobe kunit-example-test