.. SPDX-License-Identifier: GPL-2.0

==================
KUnit Architecture
==================

The KUnit architecture can be divided into two parts:

- Kernel testing library
- kunit_tool (Command line test harness)

In-Kernel Testing Framework
===========================

The kernel testing library supports KUnit tests written in C using
KUnit. KUnit tests are kernel code. KUnit does several things:

- Organizes tests
- Reports test results
- Provides test utilities

Test Cases
----------

The fundamental unit in KUnit is the test case. The KUnit test cases are
grouped into KUnit suites. A KUnit test case is a function with type
signature ``void (*)(struct kunit *test)``.
These test case functions are wrapped in a struct called
struct kunit_case.

.. note:
	``generate_params`` is optional for non-parameterized tests.

Each KUnit test case gets a ``struct kunit`` context
object passed to it that tracks a running test. The KUnit assertion
macros and other KUnit utilities use the ``struct kunit`` context
object. As an exception, there are two fields:

- ``->priv``: The setup functions can use it to store arbitrary test
  user data.

- ``->param_value``: It contains the parameter value which can be
  retrieved in the parameterized tests.

Test Suites
-----------

A KUnit suite includes a collection of test cases. The KUnit suites
are represented by the ``struct kunit_suite``. For example:

.. code-block:: c

	static struct kunit_case example_test_cases[] = {
		KUNIT_CASE(example_test_foo),
		KUNIT_CASE(example_test_bar),
		KUNIT_CASE(example_test_baz),
		{}
	};

	static struct kunit_suite example_test_suite = {
		.name = "example",
		.init = example_test_init,
		.exit = example_test_exit,
		.test_cases = example_test_cases,
	};
	kunit_test_suite(example_test_suite);

In the above example, the test suite ``example_test_suite``, runs the
test cases ``example_test_foo``, ``example_test_bar``, and
``example_test_baz``. Before running the test, the ``example_test_init``
is called and after running the test, ``example_test_exit`` is called.
The ``kunit_test_suite(example_test_suite)`` registers the test suite
with the KUnit test framework.

Executor
--------

The KUnit executor can list and run built-in KUnit tests on boot.
The Test suites are stored in a linker section
called ``.kunit_test_suites``. For code, see:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/asm-generic/vmlinux.lds.h?h=v5.15#n945.
The linker section consists of an array of pointers to
``struct kunit_suite``, and is populated by the ``kunit_test_suites()``
macro. To run all tests compiled into the kernel, the KUnit executor
iterates over the linker section array.

.. kernel-figure:: kunit_suitememorydiagram.svg
	:alt:	KUnit Suite Memory

	KUnit Suite Memory Diagram

On the kernel boot, the KUnit executor uses the start and end addresses
of this section to iterate over and run all tests. For code, see:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/kunit/executor.c

When built as a module, the ``kunit_test_suites()`` macro defines a
``module_init()`` function, which runs all the tests in the compilation
unit instead of utilizing the executor.

In KUnit tests, some error classes do not affect other tests
or parts of the kernel, each KUnit case executes in a separate thread
context. For code, see:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/kunit/try-catch.c?h=v5.15#n58

Assertion Macros
----------------

KUnit tests verify state using expectations/assertions.
All expectations/assertions are formatted as:
``KUNIT_{EXPECT|ASSERT}_<op>[_MSG](kunit, property[, message])``

- ``{EXPECT|ASSERT}`` determines whether the check is an assertion or an
  expectation.

	- For an expectation, if the check fails, marks the test as failed
	  and logs the failure.

	- An assertion, on failure, causes the test case to terminate
	  immediately.

		- Assertions call function:
		  ``void __noreturn kunit_abort(struct kunit *)``.

		- ``kunit_abort`` calls function:
		  ``void __noreturn kunit_try_catch_throw(struct kunit_try_catch *try_catch)``.

		- ``kunit_try_catch_throw`` calls function:
		  ``void kthread_complete_and_exit(struct completion *, long) __noreturn;``
		  and terminates the special thread context.

- ``<op>`` denotes a check with options: ``TRUE`` (supplied property
  has the boolean value “true”), ``EQ`` (two supplied properties are
  equal), ``NOT_ERR_OR_NULL`` (supplied pointer is not null and does not
  contain an “err” value).

- ``[_MSG]`` prints a custom message on failure.

Test Result Reporting
---------------------
KUnit prints test results in KTAP format. KTAP is based on TAP14, see:
https://github.com/isaacs/testanything.github.io/blob/tap14/tap-version-14-specification.md.
KTAP (yet to be standardized format) works with KUnit and Kselftest.
The KUnit executor prints KTAP results to dmesg, and debugfs
(if configured).

Parameterized Tests
-------------------

Each KUnit parameterized test is associated with a collection of
parameters. The test is invoked multiple times, once for each parameter
value and the parameter is stored in the ``param_value`` field.
The test case includes a KUNIT_CASE_PARAM() macro that accepts a
generator function.
The generator function is passed the previous parameter and returns the next
parameter. It also provides a macro to generate common-case generators based on
arrays.

kunit_tool (Command Line Test Harness)
======================================

kunit_tool is a Python script ``(tools/testing/kunit/kunit.py)``
that can be used to configure, build, exec, parse and run (runs other
commands in order) test results. You can either run KUnit tests using
kunit_tool or can include KUnit in kernel and parse manually.

- ``configure`` command generates the kernel ``.config`` from a
  ``.kunitconfig`` file (and any architecture-specific options).
  For some architectures, additional config options are specified in the
  ``qemu_config`` Python script
  (For example: ``tools/testing/kunit/qemu_configs/powerpc.py``).
  It parses both the existing ``.config`` and the ``.kunitconfig`` files
  and ensures that ``.config`` is a superset of ``.kunitconfig``.
  If this is not the case, it will combine the two and run
  ``make olddefconfig`` to regenerate the ``.config`` file. It then
  verifies that ``.config`` is now a superset. This checks if all
  Kconfig dependencies are correctly specified in ``.kunitconfig``.
  ``kunit_config.py`` includes the parsing Kconfigs code. The code which
  runs ``make olddefconfig`` is a part of ``kunit_kernel.py``. You can
  invoke this command via: ``./tools/testing/kunit/kunit.py config`` and
  generate a ``.config`` file.
- ``build`` runs ``make`` on the kernel tree with required options
  (depends on the architecture and some options, for example: build_dir)
  and reports any errors.
  To build a KUnit kernel from the current ``.config``, you can use the
  ``build`` argument: ``./tools/testing/kunit/kunit.py build``.
- ``exec`` command executes kernel results either directly (using
  User-mode Linux configuration), or via an emulator such
  as QEMU. It reads results from the log via standard
  output (stdout), and passes them to ``parse`` to be parsed.
  If you already have built a kernel with built-in KUnit tests,
  you can run the kernel and display the test results with the ``exec``
  argument: ``./tools/testing/kunit/kunit.py exec``.
- ``parse`` extracts the KTAP output from a kernel log, parses
  the test results, and prints a summary. For failed tests, any
  diagnostic output will be included.