Add a section on advantages of unit testing, how to write unit tests, KUnit features and Prerequisites.
Signed-off-by: Harinder Singh sharinder@google.com --- Documentation/dev-tools/kunit/index.rst | 166 +++++++++++++----------- 1 file changed, 88 insertions(+), 78 deletions(-)
diff --git a/Documentation/dev-tools/kunit/index.rst b/Documentation/dev-tools/kunit/index.rst index cacb35ec658d..55d2444b0745 100644 --- a/Documentation/dev-tools/kunit/index.rst +++ b/Documentation/dev-tools/kunit/index.rst @@ -1,11 +1,12 @@ .. SPDX-License-Identifier: GPL-2.0
-========================================= -KUnit - Unit Testing for the Linux Kernel -========================================= +================================= +KUnit - Linux Kernel Unit Testing +=================================
.. toctree:: :maxdepth: 2 + :caption: Contents:
start usage @@ -16,82 +17,91 @@ KUnit - Unit Testing for the Linux Kernel tips running_tips
-What is KUnit? -============== - -KUnit is a lightweight unit testing and mocking framework for the Linux kernel. - -KUnit is heavily inspired by JUnit, Python's unittest.mock, and -Googletest/Googlemock for C++. KUnit provides facilities for defining unit test -cases, grouping related test cases into test suites, providing common -infrastructure for running tests, and much more. - -KUnit consists of a kernel component, which provides a set of macros for easily -writing unit tests. Tests written against KUnit will run on kernel boot if -built-in, or when loaded if built as a module. These tests write out results to -the kernel log in `TAP https://testanything.org/`_ format. - -To make running these tests (and reading the results) easier, KUnit offers -:doc:`kunit_tool <kunit-tool>`, which builds a `User Mode Linux -http://user-mode-linux.sourceforge.net`_ kernel, runs it, and parses the test -results. This provides a quick way of running KUnit tests during development, -without requiring a virtual machine or separate hardware. - -Get started now: Documentation/dev-tools/kunit/start.rst - -Why KUnit? -========== - -A unit test is supposed to test a single unit of code in isolation, hence the -name. A unit test should be the finest granularity of testing and as such should -allow all possible code paths to be tested in the code under test; this is only -possible if the code under test is very small and does not have any external -dependencies outside of the test's control like hardware. - -KUnit provides a common framework for unit tests within the kernel. - -KUnit tests can be run on most architectures, and most tests are architecture -independent. All built-in KUnit tests run on kernel startup. Alternatively, -KUnit and KUnit tests can be built as modules and tests will run when the test -module is loaded. - -.. note:: - - KUnit can also run tests without needing a virtual machine or actual - hardware under User Mode Linux. User Mode Linux is a Linux architecture, - like ARM or x86, which compiles the kernel as a Linux executable. KUnit - can be used with UML either by building with ``ARCH=um`` (like any other - architecture), or by using :doc:`kunit_tool <kunit-tool>`. - -KUnit is fast. Excluding build time, from invocation to completion KUnit can run -several dozen tests in only 10 to 20 seconds; this might not sound like a big -deal to some people, but having such fast and easy to run tests fundamentally -changes the way you go about testing and even writing code in the first place. -Linus himself said in his `git talk at Google -https://gist.github.com/lorn/1272686/revisions#diff-53c65572127855f1b003db4064a94573R874`_: - - "... a lot of people seem to think that performance is about doing the - same thing, just doing it faster, and that is not true. That is not what - performance is all about. If you can do something really fast, really - well, people will start using it differently." - -In this context Linus was talking about branching and merging, -but this point also applies to testing. If your tests are slow, unreliable, are -difficult to write, and require a special setup or special hardware to run, -then you wait a lot longer to write tests, and you wait a lot longer to run -tests; this means that tests are likely to break, unlikely to test a lot of -things, and are unlikely to be rerun once they pass. If your tests are really -fast, you run them all the time, every time you make a change, and every time -someone sends you some code. Why trust that someone ran all their tests -correctly on every change when you can just run them yourself in less time than -it takes to read their test log? +This section details the kernel unit testing framework. + +Introduction +============ + +KUnit (Kernel unit testing framework) provides a common framework for +unit tests within the Linux kernel. Using KUnit, you can define groups +of test cases called test suites. The tests either run on kernel boot +if built-in, or load as a module. KUnit automatically flags and reports +failed test cases in the kernel log. The test results appear in `TAP +(Test Anything Protocol) format https://testanything.org/`_. It is inspired by +JUnit, Python’s unittest.mock, and GoogleTest/GoogleMock (C++ unit testing +framework). + +KUnit tests are part of the kernel, written in the C (programming) +language, and test parts of the Kernel implementation (example: a C +language function). Excluding build time, from invocation to +completion, KUnit can run around 100 tests in less than 10 seconds. +KUnit can test any kernel component, for example: file system, system +calls, memory management, device drivers and so on. + +KUnit follows the white-box testing approach. The test has access to +internal system functionality. KUnit runs in kernel space and is not +restricted to things exposed to user-space. + +In addition, KUnit has kunit_tool, a script (``tools/testing/kunit/kunit.py``) +that configures the Linux kernel, runs KUnit tests under QEMU or UML (`User Mode +Linux http://user-mode-linux.sourceforge.net/`_), parses the test results and +displays them in a user friendly manner. + +Features +-------- + +- Provides a framework for writing unit tests. +- Runs tests on any kernel architecture. +- Runs a test in milliseconds. + +Prerequisites +------------- + +- Any Linux kernel compatible hardware. +- For Kernel under test, Linux kernel version 5.5 or greater. + +Unit Testing +============ + +A unit test tests a single unit of code in isolation. A unit test is the finest +granularity of testing and allows all possible code paths to be tested in the +code under test. This is possible if the code under test is small and does not +have any external dependencies outside of the test's control like hardware. + + +Write Unit Tests +---------------- + +To write good unit tests, there is a simple but powerful pattern: +Arrange-Act-Assert. This is a great way to structure test cases and +defines an order of operations. + +- Arrange inputs and targets: At the start of the test, arrange the data + that allows a function to work. Example: initialize a statement or + object. +- Act on the target behavior: Call your function/code under test. +- Assert expected outcome: Verify that the result (or resulting state) is as + expected. + +Unit Testing Advantages +----------------------- + +- Increases testing speed and development in the long run. +- Detects bugs at initial stage and therefore decreases bug fix cost + compared to acceptance testing. +- Improves code quality. +- Encourages writing testable code.
How do I use it? ================
-* Documentation/dev-tools/kunit/start.rst - for new users of KUnit -* Documentation/dev-tools/kunit/tips.rst - for short examples of best practices -* Documentation/dev-tools/kunit/usage.rst - for a more detailed explanation of KUnit features -* Documentation/dev-tools/kunit/api/index.rst - for the list of KUnit APIs used for testing -* Documentation/dev-tools/kunit/kunit-tool.rst - for more information on the kunit_tool helper script -* Documentation/dev-tools/kunit/faq.rst - for answers to some common questions about KUnit +* Documentation/dev-tools/kunit/start.rst - for KUnit new users. +* Documentation/dev-tools/kunit/usage.rst - KUnit features. +* Documentation/dev-tools/kunit/tips.rst - best practices with + examples. +* Documentation/dev-tools/kunit/api/index.rst - KUnit APIs + used for testing. +* Documentation/dev-tools/kunit/kunit-tool.rst - kunit_tool helper + script. +* Documentation/dev-tools/kunit/faq.rst - KUnit common questions and + answers.