1.. SPDX-License-Identifier: GPL-2.0 2 3========================================= 4KUnit - Unit Testing for the Linux Kernel 5========================================= 6 7.. toctree:: 8 :maxdepth: 2 9 10 start 11 usage 12 kunit-tool 13 api/index 14 style 15 faq 16 17What is KUnit? 18============== 19 20KUnit is a lightweight unit testing and mocking framework for the Linux kernel. 21 22KUnit is heavily inspired by JUnit, Python's unittest.mock, and 23Googletest/Googlemock for C++. KUnit provides facilities for defining unit test 24cases, grouping related test cases into test suites, providing common 25infrastructure for running tests, and much more. 26 27KUnit consists of a kernel component, which provides a set of macros for easily 28writing unit tests. Tests written against KUnit will run on kernel boot if 29built-in, or when loaded if built as a module. These tests write out results to 30the kernel log in `TAP <https://testanything.org/>`_ format. 31 32To make running these tests (and reading the results) easier, KUnit offers 33:doc:`kunit_tool <kunit-tool>`, which builds a `User Mode Linux 34<http://user-mode-linux.sourceforge.net>`_ kernel, runs it, and parses the test 35results. This provides a quick way of running KUnit tests during development, 36without requiring a virtual machine or separate hardware. 37 38Get started now: :doc:`start` 39 40Why KUnit? 41========== 42 43A unit test is supposed to test a single unit of code in isolation, hence the 44name. A unit test should be the finest granularity of testing and as such should 45allow all possible code paths to be tested in the code under test; this is only 46possible if the code under test is very small and does not have any external 47dependencies outside of the test's control like hardware. 48 49KUnit provides a common framework for unit tests within the kernel. 50 51KUnit tests can be run on most architectures, and most tests are architecture 52independent. All built-in KUnit tests run on kernel startup. Alternatively, 53KUnit and KUnit tests can be built as modules and tests will run when the test 54module is loaded. 55 56.. note:: 57 58 KUnit can also run tests without needing a virtual machine or actual 59 hardware under User Mode Linux. User Mode Linux is a Linux architecture, 60 like ARM or x86, which compiles the kernel as a Linux executable. KUnit 61 can be used with UML either by building with ``ARCH=um`` (like any other 62 architecture), or by using :doc:`kunit_tool <kunit-tool>`. 63 64KUnit is fast. Excluding build time, from invocation to completion KUnit can run 65several dozen tests in only 10 to 20 seconds; this might not sound like a big 66deal to some people, but having such fast and easy to run tests fundamentally 67changes the way you go about testing and even writing code in the first place. 68Linus himself said in his `git talk at Google 69<https://gist.github.com/lorn/1272686/revisions#diff-53c65572127855f1b003db4064a94573R874>`_: 70 71 "... a lot of people seem to think that performance is about doing the 72 same thing, just doing it faster, and that is not true. That is not what 73 performance is all about. If you can do something really fast, really 74 well, people will start using it differently." 75 76In this context Linus was talking about branching and merging, 77but this point also applies to testing. If your tests are slow, unreliable, are 78difficult to write, and require a special setup or special hardware to run, 79then you wait a lot longer to write tests, and you wait a lot longer to run 80tests; this means that tests are likely to break, unlikely to test a lot of 81things, and are unlikely to be rerun once they pass. If your tests are really 82fast, you run them all the time, every time you make a change, and every time 83someone sends you some code. Why trust that someone ran all their tests 84correctly on every change when you can just run them yourself in less time than 85it takes to read their test log? 86 87How do I use it? 88================ 89 90* :doc:`start` - for new users of KUnit 91* :doc:`usage` - for a more detailed explanation of KUnit features 92* :doc:`api/index` - for the list of KUnit APIs used for testing 93* :doc:`kunit-tool` - for more information on the kunit_tool helper script 94* :doc:`faq` - for answers to some common questions about KUnit 95