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.

KUnit Wrapper

Included with KUnit is a simple Python wrapper that helps format the output to easily use and read KUnit output. It handles building and running the kernel, as well as formatting the output.

The wrapper can be run with:

./tools/testing/kunit/kunit.py run --defconfig

For more information on this wrapper (also called kunit_tool) checkout the kunit_tool How-To page.

Creating a .kunitconfig

The Python script is a thin wrapper around Kbuild. As such, it needs to be configured with a .kunitconfig file. This file essentially contains the regular Kernel config, with the specific test targets as well.

cd $PATH_TO_LINUX_REPO
cp arch/um/configs/kunit_defconfig .kunitconfig

Verifying KUnit Works

To make sure that everything is set up correctly, simply invoke the Python wrapper from your kernel repo:

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

Note

You may want to run make mrproper first.

If everything worked correctly, you should see the following:

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

followed by a list of tests that are run. All of them should be passing.

Note

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

Writing your first test

In your kernel repo let's add some code that we can test. Create a file drivers/misc/example.h with the contents:

int misc_example_add(int left, int right);

create a file drivers/misc/example.c:

#include <linux/errno.h>

#include "example.h"

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

Now add the following lines to drivers/misc/Kconfig:

config MISC_EXAMPLE
        bool "My example"

and the following lines to drivers/misc/Makefile:

obj-$(CONFIG_MISC_EXAMPLE) += example.o

Now we are ready to write the test. The test will be 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[] = {
        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);

Now add the following to drivers/misc/Kconfig:

config MISC_EXAMPLE_TEST
        bool "Test for my example"
        depends on MISC_EXAMPLE && KUNIT

and the following to drivers/misc/Makefile:

obj-$(CONFIG_MISC_EXAMPLE_TEST) += example-test.o

Now add it to your .kunitconfig:

CONFIG_MISC_EXAMPLE=y
CONFIG_MISC_EXAMPLE_TEST=y

Now you can run the test:

./tools/testing/kunit/kunit.py 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

  • Check out the Using KUnit page for a more in-depth explanation of KUnit.