Getting Started

This page contains an overview of the kunit_tool and KUnit framework, teaching how to run existing tests and then how to write a simple test case, and covers common problems users face when using KUnit for the first time.

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:

./tools/testing/kunit/ run


You may see the following error: "The source tree is not clean, please run 'make ARCH=um mrproper'"

This happens because internally specifies .kunit (default option) as the build directory in the command make O=output/dir through the argument --build_dir. Hence, before starting an out-of-tree build, the source tree must be clean.

There is also the same caveat mentioned in the "Build directory for the kernel" section of the admin-guide, that is, its use, it must be used for all invocations of make. The good news is that it can indeed be solved by running make ARCH=um mrproper, just be aware that this will delete the current configuration and all generated files.

If everything worked correctly, you should see the following:

Configuring KUnit Kernel ...
Building KUnit Kernel ...
Starting KUnit Kernel ...

The tests will pass or fail.


Because it is building a lot of sources for the first time, the Building KUnit Kernel step may take a while.

For detailed information on this wrapper, see: Running tests with kunit_tool.

Selecting which tests to run

By default, kunit_tool runs all tests reachable with minimal configuration, that is, using default values for most of the kconfig options. However, you can select which tests to run by:

Customizing Kconfig

A good starting point for the .kunitconfig is the KUnit default config. If you didn't run run yet, you can generate it by running:

tools/testing/kunit/ config
cat .kunit/.kunitconfig


.kunitconfig lives in the --build_dir used by, which is .kunit by default.

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.

There are many ways to customize the configurations:

  1. Edit .kunit/.kunitconfig. The file should contain the list of kconfig options required to run the desired tests, including their dependencies. 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. If you need to run on an architecture other than UML see Running tests on QEMU.

  2. Enable additional kconfig options on top of .kunit/.kunitconfig. For example, to include the kernel's linked-list test you can run:

    ./tools/testing/kunit/ run \
            --kconfig_add CONFIG_LIST_KUNIT_TEST=y
  3. Provide the path of one or more .kunitconfig files from the tree. For example, to run only FAT_FS and EXT4 tests you can run:

    ./tools/testing/kunit/ run \
            --kunitconfig ./fs/fat/.kunitconfig \
            --kunitconfig ./fs/ext4/.kunitconfig
  4. If you change the .kunitconfig, 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, won't overwrite your changes.


To save a .kunitconfig after finding a satisfactory configuration:

make savedefconfig O=.kunit
cp .kunit/defconfig .kunit/.kunitconfig

Filtering tests by name

If you want to be more specific than Kconfig can provide, it is also possible to select which tests to execute at boot-time by passing a glob filter (read instructions regarding the pattern in the manpage glob(7)). If there is a "." (period) in the filter, it will be interpreted as a separator between the name of the test suite and the test case, otherwise, it will be interpreted as the name of the test suite. For example, let's assume we are using the default config:

  1. inform the name of a test suite, like "kunit_executor_test", to run every test case it contains:

    ./tools/testing/kunit/ run "kunit_executor_test"
  2. inform the name of a test case prefixed by its test suite, like "example.example_simple_test", to run specifically that test case:

    ./tools/testing/kunit/ run "example.example_simple_test"
  3. use wildcard characters (*?[) to run any test case that matches the pattern, like "*.*64*" to run test cases containing "64" in the name inside any test suite:

    ./tools/testing/kunit/ run "*.*64*"

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.


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.


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:

int misc_example_add(int left, int right);
  1. Create a file drivers/misc/example.c, which includes:

#include <linux/errno.h>

#include "example.h"

int misc_example_add(int left, int right)
        return left + right;
  1. Add the following lines to drivers/misc/Kconfig:

        bool "My example"
  1. Add the following lines to drivers/misc/Makefile:

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:

#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[] = {

static struct kunit_suite misc_example_test_suite = {
        .name = "misc-example",
        .test_cases = misc_example_test_cases,

  1. Add the following lines to drivers/misc/Kconfig:

        tristate "Test for my example" if !KUNIT_ALL_TESTS
        depends on MISC_EXAMPLE && KUNIT
        default KUNIT_ALL_TESTS

Note: If your test does not support being built as a loadable module (which is discouraged), replace tristate by bool, and depend on KUNIT=y instead of KUNIT.

  1. Add the following lines to drivers/misc/Makefile:

obj-$(CONFIG_MISC_EXAMPLE_TEST) += example_test.o
  1. Add the following lines to .kunit/.kunitconfig:

  1. Run the test:

./tools/testing/kunit/ run

You should see the following failure:

[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

If you're interested in using some of the more advanced features of, take a look at Running tests with kunit_tool

If you'd like to run tests without using, check out Run Tests without kunit_tool

For more information on writing KUnit tests (including some common techniques for testing different things), see Writing Tests