1 .. SPDX-License-Identifier: GPL-2.0 2 3 ========================== 4 Frequently Asked Questions 5 ========================== 6 7 How is this different from Autotest, kselftest, and so on? 8 ========================================================== 9 KUnit is a unit testing framework. Autotest, kselftest (and some others) are 10 not. 11 12 A `unit test <https://martinfowler.com/bliki/UnitTest.html>`_ is supposed to 13 test a single unit of code in isolation and hence the name *unit test*. A unit 14 test should be the finest granularity of testing and should allow all possible 15 code paths to be tested in the code under test. This is only possible if the 16 code under test is small and does not have any external dependencies outside of 17 the test's control like hardware. 18 19 There are no testing frameworks currently available for the kernel that do not 20 require installing the kernel on a test machine or in a virtual machine. All 21 testing frameworks require tests to be written in userspace and run on the 22 kernel under test. This is true for Autotest, kselftest, and some others, 23 disqualifying any of them from being considered unit testing frameworks. 24 25 Does KUnit support running on architectures other than UML? 26 =========================================================== 27 28 Yes, mostly. 29 30 For the most part, the KUnit core framework (what we use to write the tests) 31 can compile to any architecture. It compiles like just another part of the 32 kernel and runs when the kernel boots, or when built as a module, when the 33 module is loaded. However, there is infrastructure, like the KUnit Wrapper 34 (``tools/testing/kunit/kunit.py``) that might not support some architectures 35 (see :ref:`kunit-on-qemu`). 36 37 In short, yes, you can run KUnit on other architectures, but it might require 38 more work than using KUnit on UML. 39 40 For more information, see :ref:`kunit-on-non-uml`. 41 42 .. _kinds-of-tests: 43 44 What is the difference between a unit test and other kinds of tests? 45 ==================================================================== 46 Most existing tests for the Linux kernel would be categorized as an integration 47 test, or an end-to-end test. 48 49 - A unit test is supposed to test a single unit of code in isolation. A unit 50 test should be the finest granularity of testing and, as such, allows all 51 possible code paths to be tested in the code under test. This is only possible 52 if the code under test is small and does not have any external dependencies 53 outside of the test's control like hardware. 54 - An integration test tests the interaction between a minimal set of components, 55 usually just two or three. For example, someone might write an integration 56 test to test the interaction between a driver and a piece of hardware, or to 57 test the interaction between the userspace libraries the kernel provides and 58 the kernel itself. However, one of these tests would probably not test the 59 entire kernel along with hardware interactions and interactions with the 60 userspace. 61 - An end-to-end test usually tests the entire system from the perspective of the 62 code under test. For example, someone might write an end-to-end test for the 63 kernel by installing a production configuration of the kernel on production 64 hardware with a production userspace and then trying to exercise some behavior 65 that depends on interactions between the hardware, the kernel, and userspace. 66 67 KUnit is not working, what should I do? 68 ======================================= 69 70 Unfortunately, there are a number of things which can break, but here are some 71 things to try. 72 73 1. Run ``./tools/testing/kunit/kunit.py run`` with the ``--raw_output`` 74 parameter. This might show details or error messages hidden by the kunit_tool 75 parser. 76 2. Instead of running ``kunit.py run``, try running ``kunit.py config``, 77 ``kunit.py build``, and ``kunit.py exec`` independently. This can help track 78 down where an issue is occurring. (If you think the parser is at fault, you 79 can run it manually against ``stdin`` or a file with ``kunit.py parse``.) 80 3. Running the UML kernel directly can often reveal issues or error messages, 81 ``kunit_tool`` ignores. This should be as simple as running ``./vmlinux`` 82 after building the UML kernel (for example, by using ``kunit.py build``). 83 Note that UML has some unusual requirements (such as the host having a tmpfs 84 filesystem mounted), and has had issues in the past when built statically and 85 the host has KASLR enabled. (On older host kernels, you may need to run 86 ``setarch `uname -m` -R ./vmlinux`` to disable KASLR.) 87 4. Make sure the kernel .config has ``CONFIG_KUNIT=y`` and at least one test 88 (e.g. ``CONFIG_KUNIT_EXAMPLE_TEST=y``). kunit_tool will keep its .config 89 around, so you can see what config was used after running ``kunit.py run``. 90 It also preserves any config changes you might make, so you can 91 enable/disable things with ``make ARCH=um menuconfig`` or similar, and then 92 re-run kunit_tool. 93 5. Try to run ``make ARCH=um defconfig`` before running ``kunit.py run``. This 94 may help clean up any residual config items which could be causing problems. 95 6. Finally, try running KUnit outside UML. KUnit and KUnit tests can be 96 built into any kernel, or can be built as a module and loaded at runtime. 97 Doing so should allow you to determine if UML is causing the issue you're 98 seeing. When tests are built-in, they will execute when the kernel boots, and 99 modules will automatically execute associated tests when loaded. Test results 100 can be collected from ``/sys/kernel/debug/kunit/<test suite>/results``, and 101 can be parsed with ``kunit.py parse``. For more details, see :ref:`kunit-on-qemu`. 102 103 If none of the above tricks help, you are always welcome to email any issues to 104 kunit-dev@googlegroups.com.
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