95 lines
4.1 KiB
ReStructuredText
95 lines
4.1 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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=========================================
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KUnit - Unit Testing for the Linux Kernel
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=========================================
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.. toctree::
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:maxdepth: 2
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start
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usage
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kunit-tool
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api/index
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style
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faq
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What is KUnit?
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==============
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KUnit is a lightweight unit testing and mocking framework for the Linux kernel.
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KUnit is heavily inspired by JUnit, Python's unittest.mock, and
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Googletest/Googlemock for C++. KUnit provides facilities for defining unit test
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cases, grouping related test cases into test suites, providing common
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infrastructure for running tests, and much more.
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KUnit consists of a kernel component, which provides a set of macros for easily
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writing unit tests. Tests written against KUnit will run on kernel boot if
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built-in, or when loaded if built as a module. These tests write out results to
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the kernel log in `TAP <https://testanything.org/>`_ format.
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To make running these tests (and reading the results) easier, KUnit offers
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:doc:`kunit_tool <kunit-tool>`, which builds a `User Mode Linux
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<http://user-mode-linux.sourceforge.net>`_ kernel, runs it, and parses the test
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results. This provides a quick way of running KUnit tests during development,
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without requiring a virtual machine or separate hardware.
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Get started now: :doc:`start`
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Why KUnit?
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==========
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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 should
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allow all possible code paths to be tested in the code under test; this is only
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possible if the code under test is very small and does not have any external
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dependencies outside of the test's control like hardware.
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KUnit provides a common framework for unit tests within the kernel.
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KUnit tests can be run on most architectures, and most tests are architecture
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independent. All built-in KUnit tests run on kernel startup. Alternatively,
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KUnit and KUnit tests can be built as modules and tests will run when the test
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module is loaded.
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.. note::
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KUnit can also run tests without needing a virtual machine or actual
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hardware under User Mode Linux. User Mode Linux is a Linux architecture,
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like ARM or x86, which compiles the kernel as a Linux executable. KUnit
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can be used with UML either by building with ``ARCH=um`` (like any other
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architecture), or by using :doc:`kunit_tool <kunit-tool>`.
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KUnit is fast. Excluding build time, from invocation to completion KUnit can run
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several dozen tests in only 10 to 20 seconds; this might not sound like a big
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deal to some people, but having such fast and easy to run tests fundamentally
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changes the way you go about testing and even writing code in the first place.
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Linus himself said in his `git talk at Google
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<https://gist.github.com/lorn/1272686/revisions#diff-53c65572127855f1b003db4064a94573R874>`_:
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"... a lot of people seem to think that performance is about doing the
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same thing, just doing it faster, and that is not true. That is not what
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performance is all about. If you can do something really fast, really
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well, people will start using it differently."
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In this context Linus was talking about branching and merging,
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but this point also applies to testing. If your tests are slow, unreliable, are
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difficult to write, and require a special setup or special hardware to run,
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then you wait a lot longer to write tests, and you wait a lot longer to run
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tests; this means that tests are likely to break, unlikely to test a lot of
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things, and are unlikely to be rerun once they pass. If your tests are really
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fast, you run them all the time, every time you make a change, and every time
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someone sends you some code. Why trust that someone ran all their tests
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correctly on every change when you can just run them yourself in less time than
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it takes to read their test log?
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How do I use it?
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================
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* :doc:`start` - for new users of KUnit
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* :doc:`usage` - for a more detailed explanation of KUnit features
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* :doc:`api/index` - for the list of KUnit APIs used for testing
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* :doc:`kunit-tool` - for more information on the kunit_tool helper script
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* :doc:`faq` - for answers to some common questions about KUnit
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