Documentation/dev-tools/kunit/start.rst

.. SPDX-License-Identifier: GPL-2.0

===============
Getting Started
===============

Installing Dependencies
=======================
KUnit has the same dependencies as the Linux kernel. As long as you can
build the kernel, you can run KUnit.

Running tests with kunit_tool
=============================
kunit_tool is a Python script, which configures and builds a kernel, runs
tests, and formats the test results. From the kernel repository, you
can run kunit_tool:

.. code-block:: bash

	./tools/testing/kunit/kunit.py run

For more information on this wrapper, see:
Documentation/dev-tools/kunit/run_wrapper.rst.

Creating a ``.kunitconfig``
---------------------------

By default, kunit_tool runs a selection of tests. However, you can specify which
unit tests to run by creating a ``.kunitconfig`` file with kernel config options
that enable only a specific set of tests and their dependencies.
The ``.kunitconfig`` file contains a list of kconfig options which are required
to run the desired targets. The ``.kunitconfig`` also contains any other test
specific config options, such as test dependencies. For example: the
``FAT_FS`` tests - ``FAT_KUNIT_TEST``, depends on
``FAT_FS``. ``FAT_FS`` can be enabled by selecting either ``MSDOS_FS``
or ``VFAT_FS``. To run ``FAT_KUNIT_TEST``, the ``.kunitconfig`` has:

.. code-block:: none

	CONFIG_KUNIT=y
	CONFIG_MSDOS_FS=y
	CONFIG_FAT_KUNIT_TEST=y

1. A good starting point for the ``.kunitconfig`` is the KUnit default config.
   You can generate it by running:

.. code-block:: bash

	cd $PATH_TO_LINUX_REPO
	tools/testing/kunit/kunit.py config
	cat .kunit/.kunitconfig

.. note ::
   ``.kunitconfig`` lives in the ``--build_dir`` used by kunit.py, which is
   ``.kunit`` by default.

.. note ::
   You may want to remove CONFIG_KUNIT_ALL_TESTS from the ``.kunitconfig`` as
   it will enable a number of additional tests that you may not want.

2. You can then add any other Kconfig options, for example:

.. code-block:: none

	CONFIG_LIST_KUNIT_TEST=y

Before running the tests, kunit_tool ensures that all config options
set in ``.kunitconfig`` are set in the kernel ``.config``. It will warn
you if you have not included dependencies for the options used.

.. note ::
   If you change the ``.kunitconfig``, kunit.py will trigger a rebuild of the
   ``.config`` file. But you can edit the ``.config`` file directly or with
   tools like ``make menuconfig O=.kunit``. As long as its a superset of
   ``.kunitconfig``, kunit.py won't overwrite your changes.

Running Tests (KUnit Wrapper)
-----------------------------
1. To make sure that everything is set up correctly, invoke the Python
   wrapper from your kernel repository:

.. code-block:: bash

	./tools/testing/kunit/kunit.py run

If everything worked correctly, you should see the following:

.. code-block::

	Generating .config ...
	Building KUnit Kernel ...
	Starting KUnit Kernel ...

The tests will pass or fail.

.. note ::
   Because it is building a lot of sources for the first time, the
   ``Building KUnit kernel`` may take a while.

Running Tests without the KUnit Wrapper
=======================================
If you do not want to use the KUnit Wrapper (for example: you want code
under test to integrate with other systems, or use a different/
unsupported architecture or configuration), KUnit can be included in
any kernel, and the results are read out and parsed manually.

.. note ::
   ``CONFIG_KUNIT`` should not be enabled in a production environment.
   Enabling KUnit disables Kernel Address-Space Layout Randomization
   (KASLR), and tests may affect the state of the kernel in ways not
   suitable for production.

Configuring the Kernel
----------------------
To enable KUnit itself, you need to enable the ``CONFIG_KUNIT`` Kconfig
option (under Kernel Hacking/Kernel Testing and Coverage in
``menuconfig``). From there, you can enable any KUnit tests. They
usually have config options ending in ``_KUNIT_TEST``.

KUnit and KUnit tests can be compiled as modules. The tests in a module
will run when the module is loaded.

Running Tests (without KUnit Wrapper)
-------------------------------------
Build and run your kernel. In the kernel log, the test output is printed
out in the TAP format. This will only happen by default if KUnit/tests
are built-in. Otherwise the module will need to be loaded.

.. note ::
   Some lines and/or data may get interspersed in the TAP output.

Writing Your First Test
=======================
In your kernel repository, let's add some code that we can test.

1. Create a file ``drivers/misc/example.h``, which includes:

.. code-block:: c

	int misc_example_add(int left, int right);

2. Create a file ``drivers/misc/example.c``, which includes:

.. code-block:: c

	#include <linux/errno.h>

	#include "example.h"

	int misc_example_add(int left, int right)
	{
		return left + right;
	}

3. Add the following lines to ``drivers/misc/Kconfig``:

.. code-block:: kconfig

	config MISC_EXAMPLE
		bool "My example"

4. Add the following lines to ``drivers/misc/Makefile``:

.. code-block:: make

	obj-$(CONFIG_MISC_EXAMPLE) += example.o

Now we are ready to write the test cases.

1. Add the below test case in ``drivers/misc/example_test.c``:

.. code-block:: c

	#include <kunit/test.h>
	#include "example.h"

	/* Define the test cases. */

	static void misc_example_add_test_basic(struct kunit *test)
	{
		KUNIT_EXPECT_EQ(test, 1, misc_example_add(1, 0));
		KUNIT_EXPECT_EQ(test, 2, misc_example_add(1, 1));
		KUNIT_EXPECT_EQ(test, 0, misc_example_add(-1, 1));
		KUNIT_EXPECT_EQ(test, INT_MAX, misc_example_add(0, INT_MAX));
		KUNIT_EXPECT_EQ(test, -1, misc_example_add(INT_MAX, INT_MIN));
	}

	static void misc_example_test_failure(struct kunit *test)
	{
		KUNIT_FAIL(test, "This test never passes.");
	}

	static struct kunit_case misc_example_test_cases[] = {
		KUNIT_CASE(misc_example_add_test_basic),
		KUNIT_CASE(misc_example_test_failure),
		{}
	};

	static struct kunit_suite misc_example_test_suite = {
		.name = "misc-example",
		.test_cases = misc_example_test_cases,
	};
	kunit_test_suite(misc_example_test_suite);

2. Add the following lines to ``drivers/misc/Kconfig``:

.. code-block:: kconfig

	config MISC_EXAMPLE_TEST
		tristate "Test for my example" if !KUNIT_ALL_TESTS
		depends on MISC_EXAMPLE && KUNIT=y
		default KUNIT_ALL_TESTS

3. Add the following lines to ``drivers/misc/Makefile``:

.. code-block:: make

	obj-$(CONFIG_MISC_EXAMPLE_TEST) += example_test.o

4. Add the following lines to ``.kunitconfig``:

.. code-block:: none

	CONFIG_MISC_EXAMPLE=y
	CONFIG_MISC_EXAMPLE_TEST=y

5. Run the test:

.. code-block:: bash

	./tools/testing/kunit/kunit.py run

You should see the following failure:

.. code-block:: none

	...
	[16:08:57] [PASSED] misc-example:misc_example_add_test_basic
	[16:08:57] [FAILED] misc-example:misc_example_test_failure
	[16:08:57] EXPECTATION FAILED at drivers/misc/example-test.c:17
	[16:08:57]      This test never passes.
	...

Congrats! You just wrote your first KUnit test.

Next Steps
==========

*   Documentation/dev-tools/kunit/architecture.rst - KUnit architecture.
*   Documentation/dev-tools/kunit/run_wrapper.rst - run kunit_tool.
*   Documentation/dev-tools/kunit/run_manual.rst - run tests without kunit_tool.
*   Documentation/dev-tools/kunit/usage.rst - write tests.
*   Documentation/dev-tools/kunit/tips.rst - best practices with
    examples.
*   Documentation/dev-tools/kunit/api/index.rst - KUnit APIs
    used for testing.
*   Documentation/dev-tools/kunit/kunit-tool.rst - kunit_tool helper
    script.
*   Documentation/dev-tools/kunit/faq.rst - KUnit common questions and
    answers.