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:
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. The format
is "<suite_glob>[.test_glob]"
.
Say that we wanted to run the sysctl tests, we could do so via:
$ echo -e 'CONFIG_KUNIT=y\nCONFIG_KUNIT_ALL_TESTS=y' > .kunit/.kunitconfig
$ ./tools/testing/kunit/kunit.py run 'sysctl*'
We can filter down to just the “write” tests via:
$ echo -e 'CONFIG_KUNIT=y\nCONFIG_KUNIT_ALL_TESTS=y' > .kunit/.kunitconfig
$ ./tools/testing/kunit/kunit.py 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
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:
$ ./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.
$ ./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.
Setting kernel commandline parameters¶
You can use --kernel_args
to pass arbitrary kernel arguments, e.g.
$ ./tools/testing/kunit/kunit.py run --kernel_args=param=42 --kernel_args=param2=false
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.
This is different from the “normal” way of getting coverage information that is documented in Using gcov with the Linux kernel.
Instead of enabling CONFIG_GCOV_KERNEL=y
, we can set these options:
CONFIG_DEBUG_KERNEL=y
CONFIG_DEBUG_INFO=y
CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
CONFIG_GCOV=y
Putting it together into a copy-pastable sequence of commands:
# Append coverage options to the current config
$ ./tools/testing/kunit/kunit.py run --kunitconfig=.kunit/ --kunitconfig=tools/testing/kunit/configs/coverage_uml.config
# 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:
$ ./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:
CONFIG_KUNIT=y
CONFIG_KUNIT_EXAMPLE_TEST=y
Then we’d see output like this in dmesg signaling the test ran and passed:
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
CONFIG_KUNIT=y
CONFIG_KUNIT_EXAMPLE_TEST=m
Then after booting into our kernel, we can run the test via
$ 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.
$ ./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:
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:
$ 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 Using gcov with the Linux kernel 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.
# Reset coverage counters before running the test.
$ echo 0 > /sys/kernel/debug/gcov/reset
$ modprobe kunit-example-test