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.. SPDX-License-Identifier: GPL-2.0
Tips For Running KUnit Tests
Using `` 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/ run $@ )
.. note::
Early versions of ```` (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
`` run`` accepts an optional glob argument to filter tests. The format
is ``"<suite_glob>[.test_glob]"``.
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/ run 'sysctl*'
We can filter down to just the "write" tests via:
.. code-block:: bash
$ echo -e 'CONFIG_KUNIT=y\nCONFIG_KUNIT_ALL_TESTS=y' > .kunit/.kunitconfig
$ ./tools/testing/kunit/ run 'sysctl*.*write*'
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
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
`` 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/ 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/ 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.
Setting kernel commandline parameters
You can use ``--kernel_args`` to pass arbitrary kernel arguments, e.g.
.. code-block:: bash
$ ./tools/testing/kunit/ run --kernel_args=param=42 --kernel_args=param2=false
Generating code coverage reports under UML
.. note::
TODO( 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.
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
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/ run
# Extract the coverage information from the build dir (.kunit/)
$ lcov -t "my_kunit_tests" -o -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
If your installed version of gcc doesn't work, you can tweak the steps:
.. code-block:: bash
$ ./tools/testing/kunit/ run --make_options=CC=/usr/bin/gcc-6
$ lcov -t "my_kunit_tests" -o -c -d .kunit/ --gcov-tool=/usr/bin/gcov-6
Running tests manually
Running tests without using `` run`` is also an important use case.
Currently it's your only option if you want to test on architectures other than
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
Then we'd see output like this in dmesg signaling the test ran and passed:
.. code-block:: none
TAP version 14
# Subtest: example
# 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
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 `` 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 `` parse`` to parse dmesg for test output and print out
results in the same familiar format that `` run`` does.
.. code-block:: bash
$ ./tools/testing/kunit/ 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
The results for each suite will be exposed under
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