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, mostly. 29 30For the most part, the KUnit core framework (what we use to write the tests) 31can compile to any architecture. It compiles like just another part of the 32kernel and runs when the kernel boots, or when built as a module, when the 33module is loaded. However, there is infrastructure, like the KUnit Wrapper 34(``tools/testing/kunit/kunit.py``) that does not support other architectures. 35 36In short, yes, you can run KUnit on other architectures, but it might require 37more work than using KUnit on UML. 38 39For more information, see :ref:`kunit-on-non-uml`. 40 41What is the difference between a unit test and other kinds of tests? 42==================================================================== 43Most existing tests for the Linux kernel would be categorized as an integration 44test, or an end-to-end test. 45 46- A unit test is supposed to test a single unit of code in isolation. A unit 47 test should be the finest granularity of testing and, as such, allows all 48 possible code paths to be tested in the code under test. This is only possible 49 if the code under test is small and does not have any external dependencies 50 outside of the test's control like hardware. 51- An integration test tests the interaction between a minimal set of components, 52 usually just two or three. For example, someone might write an integration 53 test to test the interaction between a driver and a piece of hardware, or to 54 test the interaction between the userspace libraries the kernel provides and 55 the kernel itself. However, one of these tests would probably not test the 56 entire kernel along with hardware interactions and interactions with the 57 userspace. 58- An end-to-end test usually tests the entire system from the perspective of the 59 code under test. For example, someone might write an end-to-end test for the 60 kernel by installing a production configuration of the kernel on production 61 hardware with a production userspace and then trying to exercise some behavior 62 that depends on interactions between the hardware, the kernel, and userspace. 63 64KUnit is not working, what should I do? 65======================================= 66 67Unfortunately, there are a number of things which can break, but here are some 68things to try. 69 701. Run ``./tools/testing/kunit/kunit.py run`` with the ``--raw_output`` 71 parameter. This might show details or error messages hidden by the kunit_tool 72 parser. 732. Instead of running ``kunit.py run``, try running ``kunit.py config``, 74 ``kunit.py build``, and ``kunit.py exec`` independently. This can help track 75 down where an issue is occurring. (If you think the parser is at fault, you 76 can run it manually against ``stdin`` or a file with ``kunit.py parse``.) 773. Running the UML kernel directly can often reveal issues or error messages, 78 ``kunit_tool`` ignores. This should be as simple as running ``./vmlinux`` 79 after building the UML kernel (for example, by using ``kunit.py build``). 80 Note that UML has some unusual requirements (such as the host having a tmpfs 81 filesystem mounted), and has had issues in the past when built statically and 82 the host has KASLR enabled. (On older host kernels, you may need to run 83 ``setarch `uname -m` -R ./vmlinux`` to disable KASLR.) 844. Make sure the kernel .config has ``CONFIG_KUNIT=y`` and at least one test 85 (e.g. ``CONFIG_KUNIT_EXAMPLE_TEST=y``). kunit_tool will keep its .config 86 around, so you can see what config was used after running ``kunit.py run``. 87 It also preserves any config changes you might make, so you can 88 enable/disable things with ``make ARCH=um menuconfig`` or similar, and then 89 re-run kunit_tool. 905. Try to run ``make ARCH=um defconfig`` before running ``kunit.py run``. This 91 may help clean up any residual config items which could be causing problems. 926. Finally, try running KUnit outside UML. KUnit and KUnit tests can be 93 built into any kernel, or can be built as a module and loaded at runtime. 94 Doing so should allow you to determine if UML is causing the issue you're 95 seeing. When tests are built-in, they will execute when the kernel boots, and 96 modules will automatically execute associated tests when loaded. Test results 97 can be collected from ``/sys/kernel/debug/kunit/<test suite>/results``, and 98 can be parsed with ``kunit.py parse``. For more details, see "KUnit on 99 non-UML architectures" in Documentation/dev-tools/kunit/usage.rst. 100 101If none of the above tricks help, you are always welcome to email any issues to 102kunit-dev@googlegroups.com. 103