1.. SPDX-License-Identifier: GPL-2.0
2
3=================================
4KUnit - Linux Kernel Unit Testing
5=================================
6
7.. toctree::
8	:maxdepth: 2
9	:caption: Contents:
10
11	start
12	architecture
13	run_wrapper
14	run_manual
15	usage
16	api/index
17	style
18	faq
19	running_tips
20
21This section details the kernel unit testing framework.
22
23Introduction
24============
25
26KUnit (Kernel unit testing framework) provides a common framework for
27unit tests within the Linux kernel. Using KUnit, you can define groups
28of test cases called test suites. The tests either run on kernel boot
29if built-in, or load as a module. KUnit automatically flags and reports
30failed test cases in the kernel log. The test results appear in
31:doc:`KTAP (Kernel - Test Anything Protocol) format</dev-tools/ktap>`.
32It is inspired by JUnit, Python’s unittest.mock, and GoogleTest/GoogleMock
33(C++ unit testing framework).
34
35KUnit tests are part of the kernel, written in the C (programming)
36language, and test parts of the Kernel implementation (example: a C
37language function). Excluding build time, from invocation to
38completion, KUnit can run around 100 tests in less than 10 seconds.
39KUnit can test any kernel component, for example: file system, system
40calls, memory management, device drivers and so on.
41
42KUnit follows the white-box testing approach. The test has access to
43internal system functionality. KUnit runs in kernel space and is not
44restricted to things exposed to user-space.
45
46In addition, KUnit has kunit_tool, a script (``tools/testing/kunit/kunit.py``)
47that configures the Linux kernel, runs KUnit tests under QEMU or UML
48(:doc:`User Mode Linux </virt/uml/user_mode_linux_howto_v2>`),
49parses the test results and
50displays them in a user friendly manner.
51
52Features
53--------
54
55- Provides a framework for writing unit tests.
56- Runs tests on any kernel architecture.
57- Runs a test in milliseconds.
58
59Prerequisites
60-------------
61
62- Any Linux kernel compatible hardware.
63- For Kernel under test, Linux kernel version 5.5 or greater.
64
65Unit Testing
66============
67
68A unit test tests a single unit of code in isolation. A unit test is the finest
69granularity of testing and allows all possible code paths to be tested in the
70code under test. This is possible if the code under test is small and does not
71have any external dependencies outside of the test's control like hardware.
72
73
74Write Unit Tests
75----------------
76
77To write good unit tests, there is a simple but powerful pattern:
78Arrange-Act-Assert. This is a great way to structure test cases and
79defines an order of operations.
80
81- Arrange inputs and targets: At the start of the test, arrange the data
82  that allows a function to work. Example: initialize a statement or
83  object.
84- Act on the target behavior: Call your function/code under test.
85- Assert expected outcome: Verify that the result (or resulting state) is as
86  expected.
87
88Unit Testing Advantages
89-----------------------
90
91- Increases testing speed and development in the long run.
92- Detects bugs at initial stage and therefore decreases bug fix cost
93  compared to acceptance testing.
94- Improves code quality.
95- Encourages writing testable code.
96
97Read also :ref:`kinds-of-tests`.
98
99How do I use it?
100================
101
102You can find a step-by-step guide to writing and running KUnit tests in
103Documentation/dev-tools/kunit/start.rst
104
105Alternatively, feel free to look through the rest of the KUnit documentation,
106or to experiment with tools/testing/kunit/kunit.py and the example test under
107lib/kunit/kunit-example-test.c
108
109Happy testing!
110