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![Mauro Carvalho Chehab](/assets/img/avatar_default.png)
The :doc:`foo` tag is auto-generated via automarkup.py. So, use the filename at the sources, instead of :doc:`foo`. Reviewed-by: David Gow <davidgow@google.com> Acked-by: Brendan Higgins <brendanhiggins@google.com> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org> Link: https://lore.kernel.org/r/6fde409079959a95b62b9b2692503608d7ff0dbd.1623824363.git.mchehab+huawei@kernel.org Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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.. SPDX-License-Identifier: GPL-2.0
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==========================
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Frequently Asked Questions
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==========================
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How is this different from Autotest, kselftest, etc?
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====================================================
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KUnit is a unit testing framework. Autotest, kselftest (and some others) are
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not.
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A `unit test <https://martinfowler.com/bliki/UnitTest.html>`_ is supposed to
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test a single unit of code in isolation, hence the name. A unit test should be
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the finest granularity of testing and as such should allow all possible code
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paths to be tested in the code under test; this is only possible if the code
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under test is very small and does not have any external dependencies outside of
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the test's control like hardware.
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There are no testing frameworks currently available for the kernel that do not
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require installing the kernel on a test machine or in a VM and all require
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tests to be written in userspace and run on the kernel under test; this is true
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for Autotest, kselftest, and some others, disqualifying any of them from being
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considered unit testing frameworks.
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Does KUnit support running on architectures other than UML?
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===========================================================
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Yes, well, mostly.
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For the most part, the KUnit core framework (what you use to write the tests)
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can compile to any architecture; it compiles like just another part of the
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kernel and runs when the kernel boots, or when built as a module, when the
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module is loaded. However, there is some infrastructure,
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like the KUnit Wrapper (``tools/testing/kunit/kunit.py``) that does not support
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other architectures.
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In short, this means that, yes, you can run KUnit on other architectures, but
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it might require more work than using KUnit on UML.
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For more information, see :ref:`kunit-on-non-uml`.
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What is the difference between a unit test and these other kinds of tests?
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==========================================================================
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Most existing tests for the Linux kernel would be categorized as an integration
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test, or an end-to-end test.
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- A unit test is supposed to test a single unit of code in isolation, hence the
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name. A unit test should be the finest granularity of testing and as such
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should allow all possible code paths to be tested in the code under test; this
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is only possible if the code under test is very small and does not have any
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external dependencies outside of the test's control like hardware.
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- An integration test tests the interaction between a minimal set of components,
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usually just two or three. For example, someone might write an integration
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test to test the interaction between a driver and a piece of hardware, or to
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test the interaction between the userspace libraries the kernel provides and
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the kernel itself; however, one of these tests would probably not test the
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entire kernel along with hardware interactions and interactions with the
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userspace.
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- An end-to-end test usually tests the entire system from the perspective of the
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code under test. For example, someone might write an end-to-end test for the
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kernel by installing a production configuration of the kernel on production
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hardware with a production userspace and then trying to exercise some behavior
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that depends on interactions between the hardware, the kernel, and userspace.
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KUnit isn't working, what should I do?
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======================================
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Unfortunately, there are a number of things which can break, but here are some
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things to try.
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1. Try running ``./tools/testing/kunit/kunit.py run`` with the ``--raw_output``
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parameter. This might show details or error messages hidden by the kunit_tool
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parser.
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2. Instead of running ``kunit.py run``, try running ``kunit.py config``,
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``kunit.py build``, and ``kunit.py exec`` independently. This can help track
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down where an issue is occurring. (If you think the parser is at fault, you
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can run it manually against stdin or a file with ``kunit.py parse``.)
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3. Running the UML kernel directly can often reveal issues or error messages
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kunit_tool ignores. This should be as simple as running ``./vmlinux`` after
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building the UML kernel (e.g., by using ``kunit.py build``). Note that UML
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has some unusual requirements (such as the host having a tmpfs filesystem
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mounted), and has had issues in the past when built statically and the host
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has KASLR enabled. (On older host kernels, you may need to run ``setarch
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`uname -m` -R ./vmlinux`` to disable KASLR.)
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4. Make sure the kernel .config has ``CONFIG_KUNIT=y`` and at least one test
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(e.g. ``CONFIG_KUNIT_EXAMPLE_TEST=y``). kunit_tool will keep its .config
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around, so you can see what config was used after running ``kunit.py run``.
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It also preserves any config changes you might make, so you can
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enable/disable things with ``make ARCH=um menuconfig`` or similar, and then
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re-run kunit_tool.
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5. Try to run ``make ARCH=um defconfig`` before running ``kunit.py run``. This
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may help clean up any residual config items which could be causing problems.
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6. Finally, try running KUnit outside UML. KUnit and KUnit tests can be
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built into any kernel, or can be built as a module and loaded at runtime.
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Doing so should allow you to determine if UML is causing the issue you're
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seeing. When tests are built-in, they will execute when the kernel boots, and
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modules will automatically execute associated tests when loaded. Test results
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can be collected from ``/sys/kernel/debug/kunit/<test suite>/results``, and
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can be parsed with ``kunit.py parse``. For more details, see "KUnit on
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non-UML architectures" in Documentation/dev-tools/kunit/usage.rst.
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If none of the above tricks help, you are always welcome to email any issues to
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kunit-dev@googlegroups.com.
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