1.. SPDX-License-Identifier: GPL-2.0 2 3========================== 4Frequently Asked Questions 5========================== 6 7How is this different from Autotest, kselftest, and so on? 8========================================================== 9KUnit is a unit testing framework. Autotest, kselftest (and some others) are 10not. 11 12A `unit test <https://martinfowler.com/bliki/UnitTest.html>`_ is supposed to 13test a single unit of code in isolation and hence the name *unit test*. A unit 14test should be the finest granularity of testing and should allow all possible 15code paths to be tested in the code under test. This is only possible if the 16code under test is small and does not have any external dependencies outside of 17the test's control like hardware. 18 19There are no testing frameworks currently available for the kernel that do not 20require installing the kernel on a test machine or in a virtual machine. All 21testing frameworks require tests to be written in userspace and run on the 22kernel under test. This is true for Autotest, kselftest, and some others, 23disqualifying any of them from being considered unit testing frameworks. 24 25Does KUnit support running on architectures other than UML? 26=========================================================== 27 28Yes. KUnit can run on any architecture, though the kunit.py tool can only 29build and run kernels for some architectures (of which UML is the default). 30 31You can build and run tests without kunit.py at all on any architecture by 32enabling ``CONFIG_KUNIT=y`` and booting the kernel. 33See Documentation/dev-tools/kunit/run_manual.rst for more details. 34 35Alternatively, kunit.py supports many common architectures using 36cross-compilers and the qemu emulator. This can be done using the ``--arch`` 37parameter when running the tests, and the ``--cross_compile`` parameter 38when building (if the architecture is not supported by the host compiler). 39See :ref:`kunit-on-qemu` for more details. 40 41When writing tests targeting other architectures, it's worth keeping the tips 42on the :ref:`kunit-on-non-uml` page in mind. 43 44.. _kinds-of-tests: 45 46What is the difference between a unit test and other kinds of tests? 47==================================================================== 48Most existing tests for the Linux kernel would be categorized as an integration 49test, or an end-to-end test. 50 51- A unit test is supposed to test a single unit of code in isolation. A unit 52 test should be the finest granularity of testing and, as such, allows all 53 possible code paths to be tested in the code under test. This is only possible 54 if the code under test is small and does not have any external dependencies 55 outside of the test's control like hardware. 56- An integration test tests the interaction between a minimal set of components, 57 usually just two or three. For example, someone might write an integration 58 test to test the interaction between a driver and a piece of hardware, or to 59 test the interaction between the userspace libraries the kernel provides and 60 the kernel itself. However, one of these tests would probably not test the 61 entire kernel along with hardware interactions and interactions with the 62 userspace. 63- An end-to-end test usually tests the entire system from the perspective of the 64 code under test. For example, someone might write an end-to-end test for the 65 kernel by installing a production configuration of the kernel on production 66 hardware with a production userspace and then trying to exercise some behavior 67 that depends on interactions between the hardware, the kernel, and userspace. 68 69KUnit is not working, what should I do? 70======================================= 71 72Unfortunately, there are a number of things which can break, but here are some 73things to try. 74 751. Run ``./tools/testing/kunit/kunit.py run`` with the ``--raw_output`` 76 parameter. This might show details or error messages hidden by the kunit_tool 77 parser. 782. Instead of running ``kunit.py run``, try running ``kunit.py config``, 79 ``kunit.py build``, and ``kunit.py exec`` independently. This can help track 80 down where an issue is occurring. (If you think the parser is at fault, you 81 can run it manually against ``stdin`` or a file with ``kunit.py parse``.) 823. Running the UML kernel directly can often reveal issues or error messages, 83 ``kunit_tool`` ignores. This should be as simple as runningi the ``vmlinux`` 84 binary in the output directory (by default ``./.kunit/vmlinux``) after 85 building the UML kernel (for example, by using ``kunit.py build``). 86 Note that UML has some unusual requirements (such as the host having a tmpfs 87 filesystem mounted), and has had issues in the past when built statically and 88 the host has KASLR enabled. (On older host kernels, you may need to run 89 ``setarch `uname -m` -R ./vmlinux`` to disable KASLR.) 904. Try running KUnit on a different architecture by using the ``--arch`` 91 option. On an x86_64 host, using ``--arch=x86_64`` is a good first step. 925. Make sure the kernel .config has ``CONFIG_KUNIT=y`` and at least one test 93 (e.g. ``CONFIG_KUNIT_EXAMPLE_TEST=y``). kunit_tool will keep its .config 94 around, so you can see what config was used after running ``kunit.py run``. 95 It also preserves any config changes you might make, so you can 96 enable/disable things with ``make ARCH=um menuconfig`` or similar, and then 97 re-run kunit_tool. 986. Try to run ``make ARCH=um defconfig`` before running ``kunit.py run``. This 99 may help clean up any residual config items which could be causing problems. 1007. Finally, try running KUnit manually, instead of via ``kunit.py``. KUnit can 101 be built into any kernel, or can be built as a module and loaded at runtime. 102 When tests are built-in, they will execute when the kernel boots, and 103 modules will automatically execute associated tests when loaded. Test results 104 can be collected from ``/sys/kernel/debug/kunit/<test suite>/results``, and 105 can be parsed with ``kunit.py parse``. For more details, see 106 Documentation/dev-tools/kunit/run_manual.rst 107 108If none of the above tricks help, you are always welcome to email any issues to 109kunit-dev@googlegroups.com. 110