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1.. SPDX-License-Identifier: GPL-2.0
2
3===============
4Getting Started
5===============
6
7This page contains an overview of the kunit_tool and KUnit framework,
8teaching how to run existing tests and then how to write a simple test case,
9and covers common problems users face when using KUnit for the first time.
10
11Installing Dependencies
12=======================
13KUnit has the same dependencies as the Linux kernel. As long as you can
14build the kernel, you can run KUnit.
15
16Running tests with kunit_tool
17=============================
18kunit_tool is a Python script, which configures and builds a kernel, runs
19tests, and formats the test results. From the kernel repository, you
20can run kunit_tool:
21
22.. code-block:: bash
23
24 ./tools/testing/kunit/kunit.py run
25
26.. note ::
27 You may see the following error:
28 "The source tree is not clean, please run 'make ARCH=um mrproper'"
29
30 This happens because internally kunit.py specifies ``.kunit``
31 (default option) as the build directory in the command ``make O=output/dir``
32 through the argument ``--build_dir``. Hence, before starting an
33 out-of-tree build, the source tree must be clean.
34
35 There is also the same caveat mentioned in the "Build directory for
36 the kernel" section of the :doc:`admin-guide </admin-guide/README>`,
37 that is, its use, it must be used for all invocations of ``make``.
38 The good news is that it can indeed be solved by running
39 ``make ARCH=um mrproper``, just be aware that this will delete the
40 current configuration and all generated files.
41
42If everything worked correctly, you should see the following:
43
44.. code-block::
45
46 Configuring KUnit Kernel ...
47 Building KUnit Kernel ...
48 Starting KUnit Kernel ...
49
50The tests will pass or fail.
51
52.. note ::
53 Because it is building a lot of sources for the first time,
54 the ``Building KUnit Kernel`` step may take a while.
55
56For detailed information on this wrapper, see:
57Documentation/dev-tools/kunit/run_wrapper.rst.
58
59Selecting which tests to run
60----------------------------
61
62By default, kunit_tool runs all tests reachable with minimal configuration,
63that is, using default values for most of the kconfig options. However,
64you can select which tests to run by:
65
66- `Customizing Kconfig`_ used to compile the kernel, or
67- `Filtering tests by name`_ to select specifically which compiled tests to run.
68
69Customizing Kconfig
70~~~~~~~~~~~~~~~~~~~
71A good starting point for the ``.kunitconfig`` is the KUnit default config.
72If you didn't run ``kunit.py run`` yet, you can generate it by running:
73
74.. code-block:: bash
75
76 cd $PATH_TO_LINUX_REPO
77 tools/testing/kunit/kunit.py config
78 cat .kunit/.kunitconfig
79
80.. note ::
81 ``.kunitconfig`` lives in the ``--build_dir`` used by kunit.py, which is
82 ``.kunit`` by default.
83
84Before running the tests, kunit_tool ensures that all config options
85set in ``.kunitconfig`` are set in the kernel ``.config``. It will warn
86you if you have not included dependencies for the options used.
87
88There are many ways to customize the configurations:
89
90a. Edit ``.kunit/.kunitconfig``. The file should contain the list of kconfig
91 options required to run the desired tests, including their dependencies.
92 You may want to remove CONFIG_KUNIT_ALL_TESTS from the ``.kunitconfig`` as
93 it will enable a number of additional tests that you may not want.
94 If you need to run on an architecture other than UML see :ref:`kunit-on-qemu`.
95
96b. Enable additional kconfig options on top of ``.kunit/.kunitconfig``.
97 For example, to include the kernel's linked-list test you can run::
98
99 ./tools/testing/kunit/kunit.py run \
100 --kconfig_add CONFIG_LIST_KUNIT_TEST=y
101
102c. Provide the path of one or more .kunitconfig files from the tree.
103 For example, to run only ``FAT_FS`` and ``EXT4`` tests you can run::
104
105 ./tools/testing/kunit/kunit.py run \
106 --kunitconfig ./fs/fat/.kunitconfig \
107 --kunitconfig ./fs/ext4/.kunitconfig
108
109d. If you change the ``.kunitconfig``, kunit.py will trigger a rebuild of the
110 ``.config`` file. But you can edit the ``.config`` file directly or with
111 tools like ``make menuconfig O=.kunit``. As long as its a superset of
112 ``.kunitconfig``, kunit.py won't overwrite your changes.
113
114
115.. note ::
116
117 To save a .kunitconfig after finding a satisfactory configuration::
118
119 make savedefconfig O=.kunit
120 cp .kunit/defconfig .kunit/.kunitconfig
121
122Filtering tests by name
123~~~~~~~~~~~~~~~~~~~~~~~
124If you want to be more specific than Kconfig can provide, it is also possible
125to select which tests to execute at boot-time by passing a glob filter
126(read instructions regarding the pattern in the manpage :manpage:`glob(7)`).
127If there is a ``"."`` (period) in the filter, it will be interpreted as a
128separator between the name of the test suite and the test case,
129otherwise, it will be interpreted as the name of the test suite.
130For example, let's assume we are using the default config:
131
132a. inform the name of a test suite, like ``"kunit_executor_test"``,
133 to run every test case it contains::
134
135 ./tools/testing/kunit/kunit.py run "kunit_executor_test"
136
137b. inform the name of a test case prefixed by its test suite,
138 like ``"example.example_simple_test"``, to run specifically that test case::
139
140 ./tools/testing/kunit/kunit.py run "example.example_simple_test"
141
142c. use wildcard characters (``*?[``) to run any test case that matches the pattern,
143 like ``"*.*64*"`` to run test cases containing ``"64"`` in the name inside
144 any test suite::
145
146 ./tools/testing/kunit/kunit.py run "*.*64*"
147
148Running Tests without the KUnit Wrapper
149=======================================
150If you do not want to use the KUnit Wrapper (for example: you want code
151under test to integrate with other systems, or use a different/
152unsupported architecture or configuration), KUnit can be included in
153any kernel, and the results are read out and parsed manually.
154
155.. note ::
156 ``CONFIG_KUNIT`` should not be enabled in a production environment.
157 Enabling KUnit disables Kernel Address-Space Layout Randomization
158 (KASLR), and tests may affect the state of the kernel in ways not
159 suitable for production.
160
161Configuring the Kernel
162----------------------
163To enable KUnit itself, you need to enable the ``CONFIG_KUNIT`` Kconfig
164option (under Kernel Hacking/Kernel Testing and Coverage in
165``menuconfig``). From there, you can enable any KUnit tests. They
166usually have config options ending in ``_KUNIT_TEST``.
167
168KUnit and KUnit tests can be compiled as modules. The tests in a module
169will run when the module is loaded.
170
171Running Tests (without KUnit Wrapper)
172-------------------------------------
173Build and run your kernel. In the kernel log, the test output is printed
174out in the TAP format. This will only happen by default if KUnit/tests
175are built-in. Otherwise the module will need to be loaded.
176
177.. note ::
178 Some lines and/or data may get interspersed in the TAP output.
179
180Writing Your First Test
181=======================
182In your kernel repository, let's add some code that we can test.
183
1841. Create a file ``drivers/misc/example.h``, which includes:
185
186.. code-block:: c
187
188 int misc_example_add(int left, int right);
189
1902. Create a file ``drivers/misc/example.c``, which includes:
191
192.. code-block:: c
193
194 #include <linux/errno.h>
195
196 #include "example.h"
197
198 int misc_example_add(int left, int right)
199 {
200 return left + right;
201 }
202
2033. Add the following lines to ``drivers/misc/Kconfig``:
204
205.. code-block:: kconfig
206
207 config MISC_EXAMPLE
208 bool "My example"
209
2104. Add the following lines to ``drivers/misc/Makefile``:
211
212.. code-block:: make
213
214 obj-$(CONFIG_MISC_EXAMPLE) += example.o
215
216Now we are ready to write the test cases.
217
2181. Add the below test case in ``drivers/misc/example_test.c``:
219
220.. code-block:: c
221
222 #include <kunit/test.h>
223 #include "example.h"
224
225 /* Define the test cases. */
226
227 static void misc_example_add_test_basic(struct kunit *test)
228 {
229 KUNIT_EXPECT_EQ(test, 1, misc_example_add(1, 0));
230 KUNIT_EXPECT_EQ(test, 2, misc_example_add(1, 1));
231 KUNIT_EXPECT_EQ(test, 0, misc_example_add(-1, 1));
232 KUNIT_EXPECT_EQ(test, INT_MAX, misc_example_add(0, INT_MAX));
233 KUNIT_EXPECT_EQ(test, -1, misc_example_add(INT_MAX, INT_MIN));
234 }
235
236 static void misc_example_test_failure(struct kunit *test)
237 {
238 KUNIT_FAIL(test, "This test never passes.");
239 }
240
241 static struct kunit_case misc_example_test_cases[] = {
242 KUNIT_CASE(misc_example_add_test_basic),
243 KUNIT_CASE(misc_example_test_failure),
244 {}
245 };
246
247 static struct kunit_suite misc_example_test_suite = {
248 .name = "misc-example",
249 .test_cases = misc_example_test_cases,
250 };
251 kunit_test_suite(misc_example_test_suite);
252
253 MODULE_LICENSE("GPL");
254
2552. Add the following lines to ``drivers/misc/Kconfig``:
256
257.. code-block:: kconfig
258
259 config MISC_EXAMPLE_TEST
260 tristate "Test for my example" if !KUNIT_ALL_TESTS
261 depends on MISC_EXAMPLE && KUNIT
262 default KUNIT_ALL_TESTS
263
264Note: If your test does not support being built as a loadable module (which is
265discouraged), replace tristate by bool, and depend on KUNIT=y instead of KUNIT.
266
2673. Add the following lines to ``drivers/misc/Makefile``:
268
269.. code-block:: make
270
271 obj-$(CONFIG_MISC_EXAMPLE_TEST) += example_test.o
272
2734. Add the following lines to ``.kunit/.kunitconfig``:
274
275.. code-block:: none
276
277 CONFIG_MISC_EXAMPLE=y
278 CONFIG_MISC_EXAMPLE_TEST=y
279
2805. Run the test:
281
282.. code-block:: bash
283
284 ./tools/testing/kunit/kunit.py run
285
286You should see the following failure:
287
288.. code-block:: none
289
290 ...
291 [16:08:57] [PASSED] misc-example:misc_example_add_test_basic
292 [16:08:57] [FAILED] misc-example:misc_example_test_failure
293 [16:08:57] EXPECTATION FAILED at drivers/misc/example-test.c:17
294 [16:08:57] This test never passes.
295 ...
296
297Congrats! You just wrote your first KUnit test.
298
299Next Steps
300==========
301
302If you're interested in using some of the more advanced features of kunit.py,
303take a look at Documentation/dev-tools/kunit/run_wrapper.rst
304
305If you'd like to run tests without using kunit.py, check out
306Documentation/dev-tools/kunit/run_manual.rst
307
308For more information on writing KUnit tests (including some common techniques
309for testing different things), see Documentation/dev-tools/kunit/usage.rst