Merge tag 'linux-kselftest-kunit-5.10-rc1' of...

	usage

	kunit-tool

	api/index

	style

	faq

What is KUnit?

.. SPDX-License-Identifier: GPL-2.0

===========================

Test Style and Nomenclature

===========================

To make finding, writing, and using KUnit tests as simple as possible, it's

strongly encouraged that they are named and written according to the guidelines

below. While it's possible to write KUnit tests which do not follow these rules,

they may break some tooling, may conflict with other tests, and may not be run

automatically by testing systems.

It's recommended that you only deviate from these guidelines when:

1. Porting tests to KUnit which are already known with an existing name, or

2. Writing tests which would cause serious problems if automatically run (e.g.,

   non-deterministically producing false positives or negatives, or taking an

   extremely long time to run).

Subsystems, Suites, and Tests

=============================

In order to make tests as easy to find as possible, they're grouped into suites

and subsystems. A test suite is a group of tests which test a related area of

the kernel, and a subsystem is a set of test suites which test different parts

of the same kernel subsystem or driver.

Subsystems

----------

Every test suite must belong to a subsystem. A subsystem is a collection of one

or more KUnit test suites which test the same driver or part of the kernel. A

rule of thumb is that a test subsystem should match a single kernel module. If

the code being tested can't be compiled as a module, in many cases the subsystem

should correspond to a directory in the source tree or an entry in the

MAINTAINERS file. If unsure, follow the conventions set by tests in similar

areas.

Test subsystems should be named after the code being tested, either after the

module (wherever possible), or after the directory or files being tested. Test

subsystems should be named to avoid ambiguity where necessary.

If a test subsystem name has multiple components, they should be separated by

underscores. *Do not* include "test" or "kunit" directly in the subsystem name

unless you are actually testing other tests or the kunit framework itself.

Example subsystems could be:

``ext4``

  Matches the module and filesystem name.

``apparmor``

  Matches the module name and LSM name.

``kasan``

  Common name for the tool, prominent part of the path ``mm/kasan``

``snd_hda_codec_hdmi``

  Has several components (``snd``, ``hda``, ``codec``, ``hdmi``) separated by

  underscores. Matches the module name.

Avoid names like these:

``linear-ranges``

  Names should use underscores, not dashes, to separate words. Prefer

  ``linear_ranges``.

``qos-kunit-test``

  As well as using underscores, this name should not have "kunit-test" as a

  suffix, and ``qos`` is ambiguous as a subsystem name. ``power_qos`` would be a

  better name.

``pc_parallel_port``

  The corresponding module name is ``parport_pc``, so this subsystem should also

  be named ``parport_pc``.

.. note::

        The KUnit API and tools do not explicitly know about subsystems. They're

        simply a way of categorising test suites and naming modules which

        provides a simple, consistent way for humans to find and run tests. This

        may change in the future, though.

Suites

------

KUnit tests are grouped into test suites, which cover a specific area of

functionality being tested. Test suites can have shared initialisation and

shutdown code which is run for all tests in the suite.

Not all subsystems will need to be split into multiple test suites (e.g. simple drivers).

Test suites are named after the subsystem they are part of. If a subsystem

contains several suites, the specific area under test should be appended to the

subsystem name, separated by an underscore.

In the event that there are multiple types of test using KUnit within a

subsystem (e.g., both unit tests and integration tests), they should be put into

separate suites, with the type of test as the last element in the suite name.

Unless these tests are actually present, avoid using ``_test``, ``_unittest`` or

similar in the suite name.

The full test suite name (including the subsystem name) should be specified as

the ``.name`` member of the ``kunit_suite`` struct, and forms the base for the

module name (see below).

Example test suites could include:

``ext4_inode``

  Part of the ``ext4`` subsystem, testing the ``inode`` area.

``kunit_try_catch``

  Part of the ``kunit`` implementation itself, testing the ``try_catch`` area.

``apparmor_property_entry``

  Part of the ``apparmor`` subsystem, testing the ``property_entry`` area.

``kasan``

  The ``kasan`` subsystem has only one suite, so the suite name is the same as

  the subsystem name.

Avoid names like:

``ext4_ext4_inode``

  There's no reason to state the subsystem twice.

``property_entry``

  The suite name is ambiguous without the subsystem name.

``kasan_integration_test``

  Because there is only one suite in the ``kasan`` subsystem, the suite should

  just be called ``kasan``. There's no need to redundantly add

  ``integration_test``. Should a separate test suite with, for example, unit

  tests be added, then that suite could be named ``kasan_unittest`` or similar.

Test Cases

----------

Individual tests consist of a single function which tests a constrained

codepath, property, or function. In the test output, individual tests' results

will show up as subtests of the suite's results.

Tests should be named after what they're testing. This is often the name of the

function being tested, with a description of the input or codepath being tested.

As tests are C functions, they should be named and written in accordance with

the kernel coding style.

.. note::

        As tests are themselves functions, their names cannot conflict with

        other C identifiers in the kernel. This may require some creative

        naming. It's a good idea to make your test functions `static` to avoid

        polluting the global namespace.

Example test names include:

``unpack_u32_with_null_name``

  Tests the ``unpack_u32`` function when a NULL name is passed in.

``test_list_splice``

  Tests the ``list_splice`` macro. It has the prefix ``test_`` to avoid a

  name conflict with the macro itself.

Should it be necessary to refer to a test outside the context of its test suite,

the *fully-qualified* name of a test should be the suite name followed by the

test name, separated by a colon (i.e. ``suite:test``).

Test Kconfig Entries

====================

Every test suite should be tied to a Kconfig entry.

This Kconfig entry must:

* be named ``CONFIG_<name>_KUNIT_TEST``: where <name> is the name of the test

  suite.

* be listed either alongside the config entries for the driver/subsystem being

  tested, or be under [Kernel Hacking]→[Kernel Testing and Coverage]

* depend on ``CONFIG_KUNIT``

* be visible only if ``CONFIG_KUNIT_ALL_TESTS`` is not enabled.

* have a default value of ``CONFIG_KUNIT_ALL_TESTS``.

* have a brief description of KUnit in the help text

Unless there's a specific reason not to (e.g. the test is unable to be built as

a module), Kconfig entries for tests should be tristate.

An example Kconfig entry:

.. code-block:: none

        config FOO_KUNIT_TEST

                tristate "KUnit test for foo" if !KUNIT_ALL_TESTS

                depends on KUNIT

                default KUNIT_ALL_TESTS

                help

                    This builds unit tests for foo.

                    For more information on KUnit and unit tests in general, please refer

                    to the KUnit documentation in Documentation/dev-tools/kunit

                    If unsure, say N

Test File and Module Names

==========================

KUnit tests can often be compiled as a module. These modules should be named

after the test suite, followed by ``_test``. If this is likely to conflict with

non-KUnit tests, the suffix ``_kunit`` can also be used.

The easiest way of achieving this is to name the file containing the test suite

``<suite>_test.c`` (or, as above, ``<suite>_kunit.c``). This file should be

placed next to the code under test.

If the suite name contains some or all of the name of the test's parent

directory, it may make sense to modify the source filename to reduce redundancy.

For example, a ``foo_firmware`` suite could be in the ``foo/firmware_test.c``

file.

.. note::

   A test case will only be run if it is associated with a test suite.

``kunit_test_suite(...)`` is a macro which tells the linker to put the specified

test suite in a special linker section so that it can be run by KUnit either

after late_init, or when the test module is loaded (depending on whether the

test was built in or not).

For more information on these types of things see the :doc:`api/test`.

Isolating Behavior

	THERMAL_TABLE(governor)						\

	EARLYCON_TABLE()						\

	LSM_TABLE()							\

	EARLY_LSM_TABLE()

	EARLY_LSM_TABLE()						\

	KUNIT_TABLE()

#define INIT_TEXT							\

	*(.init.text .init.text.*)					\

		KEEP(*(.con_initcall.init))				\

		__con_initcall_end = .;

/* Alignment must be consistent with (kunit_suite *) in include/kunit/test.h */

#define KUNIT_TABLE()							\

		. = ALIGN(8);						\

		__kunit_suites_start = .;				\

		KEEP(*(.kunit_test_suites))				\

		__kunit_suites_end = .;

#ifdef CONFIG_BLK_DEV_INITRD

#define INIT_RAM_FS							\

	. = ALIGN(4);							\

unsigned int kunit_test_case_num(struct kunit_suite *suite,

				 struct kunit_case *test_case);

int __kunit_test_suites_init(struct kunit_suite **suites);

int __kunit_test_suites_init(struct kunit_suite * const * const suites);

void __kunit_test_suites_exit(struct kunit_suite **suites);

#if IS_BUILTIN(CONFIG_KUNIT)

int kunit_run_all_tests(void);

#else

static inline int kunit_run_all_tests(void)

{

	return 0;

}

#endif /* IS_BUILTIN(CONFIG_KUNIT) */

/**

 * kunit_test_suites() - used to register one or more &struct kunit_suite

 *			 with KUnit.

 * Registers @suites_list with the test framework. See &struct kunit_suite for

 * more information.

 *

 * When builtin, KUnit tests are all run as late_initcalls; this means

 * that they cannot test anything where tests must run at a different init

 * phase. One significant restriction resulting from this is that KUnit

 * cannot reliably test anything that is initialize in the late_init phase;

 * another is that KUnit is useless to test things that need to be run in

 * an earlier init phase.

 *

 * An alternative is to build the tests as a module.  Because modules

 * do not support multiple late_initcall()s, we need to initialize an

 * array of suites for a module.

 *

 * TODO(brendanhiggins@google.com): Don't run all KUnit tests as

 * late_initcalls.  I have some future work planned to dispatch all KUnit

 * tests from the same place, and at the very least to do so after

 * everything else is definitely initialized.

 * If a test suite is built-in, module_init() gets translated into

 * an initcall which we don't want as the idea is that for builtins

 * the executor will manage execution.  So ensure we do not define

 * module_{init|exit} functions for the builtin case when registering

 * suites via kunit_test_suites() below.

 */

#define kunit_test_suites(suites_list...)				\

	static struct kunit_suite *suites[] = {suites_list, NULL};	\

	static int kunit_test_suites_init(void)				\

#ifdef MODULE

#define kunit_test_suites_for_module(__suites)				\

	static int __init kunit_test_suites_init(void)			\

	{								\

		return __kunit_test_suites_init(suites);		\

		return __kunit_test_suites_init(__suites);		\

	}								\

	late_initcall(kunit_test_suites_init);				\

	module_init(kunit_test_suites_init);				\

									\

	static void __exit kunit_test_suites_exit(void)			\

	{								\

		return __kunit_test_suites_exit(suites);		\

		return __kunit_test_suites_exit(__suites);		\

	}								\

	module_exit(kunit_test_suites_exit)

#else

#define kunit_test_suites_for_module(__suites)

#endif /* MODULE */

#define __kunit_test_suites(unique_array, unique_suites, ...)		       \

	static struct kunit_suite *unique_array[] = { __VA_ARGS__, NULL };     \

	kunit_test_suites_for_module(unique_array);			       \

	static struct kunit_suite **unique_suites			       \

	__used __section(.kunit_test_suites) = unique_array

/**

 * kunit_test_suites() - used to register one or more &struct kunit_suite

 *			 with KUnit.

 *

 * @suites: a statically allocated list of &struct kunit_suite.

 *

 * Registers @suites with the test framework. See &struct kunit_suite for

 * more information.

 *

 * When builtin,  KUnit tests are all run via executor; this is done

 * by placing the array of struct kunit_suite * in the .kunit_test_suites

 * ELF section.

 *

 * An alternative is to build the tests as a module.  Because modules do not

 * support multiple initcall()s, we need to initialize an array of suites for a

 * module.

 *

 */

#define kunit_test_suites(...)						\

	__kunit_test_suites(__UNIQUE_ID(array),				\

			    __UNIQUE_ID(suites),			\

			    __VA_ARGS__)

#define kunit_test_suite(suite)	kunit_test_suites(&suite)