1.. SPDX-License-Identifier: GPL-2.0
2
3===========================
4Test Style and Nomenclature
5===========================
6
7To make finding, writing, and using KUnit tests as simple as possible, it's
8strongly encouraged that they are named and written according to the guidelines
9below. While it's possible to write KUnit tests which do not follow these rules,
10they may break some tooling, may conflict with other tests, and may not be run
11automatically by testing systems.
12
13It's recommended that you only deviate from these guidelines when:
14
151. Porting tests to KUnit which are already known with an existing name, or
162. Writing tests which would cause serious problems if automatically run (e.g.,
17   non-deterministically producing false positives or negatives, or taking an
18   extremely long time to run).
19
20Subsystems, Suites, and Tests
21=============================
22
23In order to make tests as easy to find as possible, they're grouped into suites
24and subsystems. A test suite is a group of tests which test a related area of
25the kernel, and a subsystem is a set of test suites which test different parts
26of the same kernel subsystem or driver.
27
28Subsystems
29----------
30
31Every test suite must belong to a subsystem. A subsystem is a collection of one
32or more KUnit test suites which test the same driver or part of the kernel. A
33rule of thumb is that a test subsystem should match a single kernel module. If
34the code being tested can't be compiled as a module, in many cases the subsystem
35should correspond to a directory in the source tree or an entry in the
36MAINTAINERS file. If unsure, follow the conventions set by tests in similar
37areas.
38
39Test subsystems should be named after the code being tested, either after the
40module (wherever possible), or after the directory or files being tested. Test
41subsystems should be named to avoid ambiguity where necessary.
42
43If a test subsystem name has multiple components, they should be separated by
44underscores. *Do not* include "test" or "kunit" directly in the subsystem name
45unless you are actually testing other tests or the kunit framework itself.
46
47Example subsystems could be:
48
49``ext4``
50  Matches the module and filesystem name.
51``apparmor``
52  Matches the module name and LSM name.
53``kasan``
54  Common name for the tool, prominent part of the path ``mm/kasan``
55``snd_hda_codec_hdmi``
56  Has several components (``snd``, ``hda``, ``codec``, ``hdmi``) separated by
57  underscores. Matches the module name.
58
59Avoid names like these:
60
61``linear-ranges``
62  Names should use underscores, not dashes, to separate words. Prefer
63  ``linear_ranges``.
64``qos-kunit-test``
65  As well as using underscores, this name should not have "kunit-test" as a
66  suffix, and ``qos`` is ambiguous as a subsystem name. ``power_qos`` would be a
67  better name.
68``pc_parallel_port``
69  The corresponding module name is ``parport_pc``, so this subsystem should also
70  be named ``parport_pc``.
71
72.. note::
73        The KUnit API and tools do not explicitly know about subsystems. They're
74        simply a way of categorising test suites and naming modules which
75        provides a simple, consistent way for humans to find and run tests. This
76        may change in the future, though.
77
78Suites
79------
80
81KUnit tests are grouped into test suites, which cover a specific area of
82functionality being tested. Test suites can have shared initialisation and
83shutdown code which is run for all tests in the suite.
84Not all subsystems will need to be split into multiple test suites (e.g. simple drivers).
85
86Test suites are named after the subsystem they are part of. If a subsystem
87contains several suites, the specific area under test should be appended to the
88subsystem name, separated by an underscore.
89
90In the event that there are multiple types of test using KUnit within a
91subsystem (e.g., both unit tests and integration tests), they should be put into
92separate suites, with the type of test as the last element in the suite name.
93Unless these tests are actually present, avoid using ``_test``, ``_unittest`` or
94similar in the suite name.
95
96The full test suite name (including the subsystem name) should be specified as
97the ``.name`` member of the ``kunit_suite`` struct, and forms the base for the
98module name (see below).
99
100Example test suites could include:
101
102``ext4_inode``
103  Part of the ``ext4`` subsystem, testing the ``inode`` area.
104``kunit_try_catch``
105  Part of the ``kunit`` implementation itself, testing the ``try_catch`` area.
106``apparmor_property_entry``
107  Part of the ``apparmor`` subsystem, testing the ``property_entry`` area.
108``kasan``
109  The ``kasan`` subsystem has only one suite, so the suite name is the same as
110  the subsystem name.
111
112Avoid names like:
113
114``ext4_ext4_inode``
115  There's no reason to state the subsystem twice.
116``property_entry``
117  The suite name is ambiguous without the subsystem name.
118``kasan_integration_test``
119  Because there is only one suite in the ``kasan`` subsystem, the suite should
120  just be called ``kasan``. There's no need to redundantly add
121  ``integration_test``. Should a separate test suite with, for example, unit
122  tests be added, then that suite could be named ``kasan_unittest`` or similar.
123
124Test Cases
125----------
126
127Individual tests consist of a single function which tests a constrained
128codepath, property, or function. In the test output, individual tests' results
129will show up as subtests of the suite's results.
130
131Tests should be named after what they're testing. This is often the name of the
132function being tested, with a description of the input or codepath being tested.
133As tests are C functions, they should be named and written in accordance with
134the kernel coding style.
135
136.. note::
137        As tests are themselves functions, their names cannot conflict with
138        other C identifiers in the kernel. This may require some creative
139        naming. It's a good idea to make your test functions `static` to avoid
140        polluting the global namespace.
141
142Example test names include:
143
144``unpack_u32_with_null_name``
145  Tests the ``unpack_u32`` function when a NULL name is passed in.
146``test_list_splice``
147  Tests the ``list_splice`` macro. It has the prefix ``test_`` to avoid a
148  name conflict with the macro itself.
149
150
151Should it be necessary to refer to a test outside the context of its test suite,
152the *fully-qualified* name of a test should be the suite name followed by the
153test name, separated by a colon (i.e. ``suite:test``).
154
155Test Kconfig Entries
156====================
157
158Every test suite should be tied to a Kconfig entry.
159
160This Kconfig entry must:
161
162* be named ``CONFIG_<name>_KUNIT_TEST``: where <name> is the name of the test
163  suite.
164* be listed either alongside the config entries for the driver/subsystem being
165  tested, or be under [Kernel Hacking]→[Kernel Testing and Coverage]
166* depend on ``CONFIG_KUNIT``
167* be visible only if ``CONFIG_KUNIT_ALL_TESTS`` is not enabled.
168* have a default value of ``CONFIG_KUNIT_ALL_TESTS``.
169* have a brief description of KUnit in the help text
170
171Unless there's a specific reason not to (e.g. the test is unable to be built as
172a module), Kconfig entries for tests should be tristate.
173
174An example Kconfig entry:
175
176.. code-block:: none
177
178        config FOO_KUNIT_TEST
179                tristate "KUnit test for foo" if !KUNIT_ALL_TESTS
180                depends on KUNIT
181                default KUNIT_ALL_TESTS
182                help
183                    This builds unit tests for foo.
184
185                    For more information on KUnit and unit tests in general, please refer
186                    to the KUnit documentation in Documentation/dev-tools/kunit
187
188                    If unsure, say N
189
190
191Test File and Module Names
192==========================
193
194KUnit tests can often be compiled as a module. These modules should be named
195after the test suite, followed by ``_test``. If this is likely to conflict with
196non-KUnit tests, the suffix ``_kunit`` can also be used.
197
198The easiest way of achieving this is to name the file containing the test suite
199``<suite>_test.c`` (or, as above, ``<suite>_kunit.c``). This file should be
200placed next to the code under test.
201
202If the suite name contains some or all of the name of the test's parent
203directory, it may make sense to modify the source filename to reduce redundancy.
204For example, a ``foo_firmware`` suite could be in the ``foo/firmware_test.c``
205file.
206