Re: [PATCH 9/9] Documentation: kunit: Document new parameterized test features

[Marie Zhussupova <marievic@google.com>]

On Sat, Aug 2, 2025 at 5:45 AM David Gow <davidgow@google.com> wrote:
>
> On Wed, 30 Jul 2025 at 03:37, Marie Zhussupova <marievic@google.com> wrote:
> >
> > -Update the KUnit documentation to explain the concept
> > of a parent parameterized test.
> > -Add examples demonstrating different ways of passing
> > parameters to parameterized tests and how to manage
> > shared resources between them.
> >
>
> Nit: We don't need the dot points ('-') here. Just make them paragraphs.

Will do!

>
> > Signed-off-by: Marie Zhussupova <marievic@google.com>
> > ---
>
> Thanks very, very much for including such detailed documentation.
>
> I do think some of the examples could be trimmed / left in the
> kunit-example-test.c file and referenced, as they're long enough that
> it's difficult to focus on the essentials. But otherwise, this looks
> great.
>
> A few small notes below, but otherwise:
>
> Reviewed-by: David Gow <davidgow@google.com>
>
> Cheers,
> -- David
>
> >  Documentation/dev-tools/kunit/usage.rst | 455 +++++++++++++++++++++++-
> >  1 file changed, 449 insertions(+), 6 deletions(-)
> >
> > diff --git a/Documentation/dev-tools/kunit/usage.rst b/Documentation/dev-tools/kunit/usage.rst
> > index 066ecda1dd98..be1d656053cf 100644
> > --- a/Documentation/dev-tools/kunit/usage.rst
> > +++ b/Documentation/dev-tools/kunit/usage.rst
> > @@ -542,11 +542,21 @@ There is more boilerplate code involved, but it can:
> >  Parameterized Testing
> >  ~~~~~~~~~~~~~~~~~~~~~
> >
> > -The table-driven testing pattern is common enough that KUnit has special
> > -support for it.
> > -
> > -By reusing the same ``cases`` array from above, we can write the test as a
> > -"parameterized test" with the following.
> > +To efficiently and elegantly validate a test case against a variety of inputs,
> > +KUnit also provides a parameterized testing framework. This feature formalizes
> > +and extends the concept of table-driven tests discussed previously, offering
> > +a more integrated and flexible way to handle multiple test scenarios with
> > +minimal code duplication.
>
> Nit: maybe we can tone down the adjectives slightly here. I do like
> parameterised testing a lot, but it probably doesn't need to be
> "efficient", "elegant", "integrated", and "flexible".

Will do that in v2.

>
> > +
> > +Passing Parameters to the Test Cases
> > +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > +There are three main ways to provide the parameters to a test case:
> > +
> > +Array Parameter Macros (``KUNIT_ARRAY_PARAM`` or ``KUNIT_ARRAY_PARAM_DESC``):
> > +   KUnit provides special support for the common table-driven testing pattern.
> > +   By applying either ``KUNIT_ARRAY_PARAM`` or ``KUNIT_ARRAY_PARAM_DESC`` to the
> > +   ``cases`` array from the previous section, we can create a parameterized test
> > +   as shown below:
> >
> >  .. code-block:: c
> >
> > @@ -555,7 +565,7 @@ By reusing the same ``cases`` array from above, we can write the test as a
> >                 const char *str;
> >                 const char *sha1;
> >         };
> > -       const struct sha1_test_case cases[] = {
> > +       static const struct sha1_test_case cases[] = {
> >                 {
> >                         .str = "hello world",
> >                         .sha1 = "2aae6c35c94fcfb415dbe95f408b9ce91ee846ed",
> > @@ -590,6 +600,439 @@ By reusing the same ``cases`` array from above, we can write the test as a
> >                 {}
> >         };
> >
> > +Custom Parameter Generator (``generate_params``):
> > +   You can pass your own ``generate_params`` function to the ``KUNIT_CASE_PARAM``
> > +   or ``KUNIT_CASE_PARAM_WITH_INIT`` macros. This function is responsible for
> > +   generating parameters one by one. It receives the previously generated parameter
> > +   as the ``prev`` argument (which is ``NULL`` on the first call) and can also
> > +   access any context available from the parent ``struct kunit`` passed as the
> > +   ``test`` argument. KUnit calls this function repeatedly until it returns
> > +   ``NULL``. Below is an example of how it works:
> > +
> > +.. code-block:: c
> > +
> > +       #define MAX_TEST_BUFFER_SIZE 8
> > +
> > +       // Example generator function. It produces a sequence of buffer sizes that
> > +       // are powers of two, starting at 1 (e.g., 1, 2, 4, 8).
> > +       static const void *buffer_size_gen_params(struct kunit *test, const void *prev, char *desc)
> > +       {
> > +               long prev_buffer_size = (long)prev;
> > +               long next_buffer_size = 1; // Start with an initial size of 1.
> > +
> > +               // Stop generating parameters if the limit is reached or exceeded.
> > +               if (prev_buffer_size >= MAX_TEST_BUFFER_SIZE)
> > +                       return NULL;
> > +
> > +               // For subsequent calls, calculate the next size by doubling the previous one.
> > +               if (prev)
> > +                       next_buffer_size = prev_buffer_size << 1;
> > +
> > +               return (void *)next_buffer_size;
> > +       }
> > +
> > +       // Simple test to validate that kunit_kzalloc provides zeroed memory.
> > +       static void buffer_zero_test(struct kunit *test)
> > +       {
> > +               long buffer_size = (long)test->param_value;
> > +               // Use kunit_kzalloc to allocate a zero-initialized buffer. This makes the
> > +               // memory "parameter managed," meaning it's automatically cleaned up at
> > +               // the end of each parameter execution.
> > +               int *buf = kunit_kzalloc(test, buffer_size * sizeof(int), GFP_KERNEL);
> > +
> > +               // Ensure the allocation was successful.
> > +               KUNIT_ASSERT_NOT_NULL(test, buf);
> > +
> > +               // Loop through the buffer and confirm every element is zero.
> > +               for (int i = 0; i < buffer_size; i++)
> > +                       KUNIT_EXPECT_EQ(test, buf[i], 0);
> > +       }
> > +
> > +       static struct kunit_case buffer_test_cases[] = {
> > +               KUNIT_CASE_PARAM(buffer_zero_test, buffer_size_gen_params),
> > +               {}
> > +       };
> > +
> > +Direct Registration in Parameter Init Function (using ``kunit_register_params_array``):
>
> Maybe we should highlight this as being array-based more explicitly.
> "Runtime Array Registration in the Init function" or similar?

That would make it clearer, will make this edit in v2.

>
> > +   For more complex scenarios, you can directly register a parameter array with
> > +   a test case instead of using a ``generate_params`` function. This is done by
> > +   passing the array to the ``kunit_register_params_array`` macro within an
> > +   initialization function for the parameterized test series
> > +   (i.e., a function named ``param_init``). To better understand this mechanism
> > +   please refer to the "Adding Shared Resources" section below.
> > +
> > +   This method supports both dynamically built and static arrays.
> > +
> > +   As the following code shows, the ``example_param_init_dynamic_arr`` function
> > +   utilizes ``make_fibonacci_params`` to create a dynamic array, which is then
> > +   registered using ``kunit_register_params_array``. The corresponding exit
> > +   function, ``example_param_exit``, is responsible for freeing this dynamically
> > +   allocated params array after the parameterized test series ends.
> > +
> > +.. code-block:: c
> > +
> > +       /*
> > +        * Helper function to create a parameter array of Fibonacci numbers. This example
> > +        * highlights a parameter generation scenario that is:
> > +        * 1. Not feasible to fully pre-generate at compile time.
> > +        * 2. Challenging to implement with a standard 'generate_params' function,
> > +        * as it typically only provides the immediately 'prev' parameter, while
> > +        * Fibonacci requires access to two preceding values for calculation.
> > +        */
> > +       static void *make_fibonacci_params(int seq_size)
> > +       {
> > +               int *seq;
> > +
> > +               if (seq_size <= 0)
> > +                       return NULL;
> > +
> > +               seq = kmalloc_array(seq_size, sizeof(int), GFP_KERNEL);
> > +
> > +               if (!seq)
> > +                       return NULL;
> > +
> > +               if (seq_size >= 1)
> > +                       seq[0] = 0;
> > +               if (seq_size >= 2)
> > +                       seq[1] = 1;
> > +               for (int i = 2; i < seq_size; i++)
> > +                       seq[i] = seq[i - 1] + seq[i - 2];
> > +               return seq;
> > +       }
> > +
> > +       // This is an example of a function that provides a description for each of the
> > +       // parameters.
> > +       static void example_param_dynamic_arr_get_desc(const void *p, char *desc)
> > +       {
> > +               const int *fib_num = p;
> > +
> > +               snprintf(desc, KUNIT_PARAM_DESC_SIZE, "fibonacci param: %d", *fib_num);
> > +       }
> > +
> > +       // Example of a parameterized test init function that registers a dynamic array.
> > +       static int example_param_init_dynamic_arr(struct kunit *test)
> > +       {
> > +               int seq_size = 6;
> > +               int *fibonacci_params = make_fibonacci_params(seq_size);
> > +
> > +               if (!fibonacci_params)
> > +                       return -ENOMEM;
> > +
> > +               /*
> > +                * Passes the dynamic parameter array information to the parent struct kunit.
> > +                * The array and its metadata will be stored in test->parent->params_data.
> > +                * The array itself will be located in params_data.params.
> > +                */
> > +               kunit_register_params_array(test, fibonacci_params, seq_size,
> > +                                           example_param_dynamic_arr_get_desc);
> > +               return 0;
> > +       }
> > +
> > +       // Function to clean up the parameterized test's parent kunit struct if
> > +       // there were custom allocations.
> > +       static void example_param_exit_dynamic_arr(struct kunit *test)
> > +       {
> > +               /*
> > +                * We allocated this array, so we need to free it.
> > +                * Since the parent parameter instance is passed here,
> > +                * we can directly access the array via `test->params_data.params`
> > +                * instead of `test->parent->params_data.params`.
> > +                */
> > +               kfree(test->params_data.params);
> > +       }
> > +
> > +       /*
> > +        * Example of test that uses the registered dynamic array to perform assertions
> > +        * and expectations.
> > +        */
> > +       static void example_params_test_with_init_dynamic_arr(struct kunit *test)
> > +       {
> > +               const int *param = test->param_value;
> > +               int param_val;
> > +
> > +               /* By design, param pointer will not be NULL. */
> > +               KUNIT_ASSERT_NOT_NULL(test, param);
> > +
> > +               param_val = *param;
> > +               KUNIT_EXPECT_EQ(test, param_val - param_val, 0);
> > +       }
> > +
> > +       static struct kunit_case example_tests[] = {
> > +               // The NULL here stands in for the generate_params function
> > +               KUNIT_CASE_PARAM_WITH_INIT(example_params_test_with_init_dynamic_arr, NULL,
> > +                                          example_param_init_dynamic_arr,
> > +                                          example_param_exit_dynamic_arr),
> > +               {}
> > +       };
> > +
>
> This is a long example, which already exists in the source code
> (kunit-example-test.c). Could we just include some highlights (e.g.,
> the init function and the KUNIT_CASE_PARAM_WITH_INIT call), and link
> to the source code for the rest?

Thank you for the suggestion! I will do that in v2.

>
> > +Adding Shared Resources
> > +^^^^^^^^^^^^^^^^^^^^^^^
> > +All parameterized test executions in this framework have a parent test of type
> > +``struct kunit``. This parent is not used to execute any test logic itself;
> > +instead, it serves as a container for shared context that can be accessed by
> > +all its individual test executions (or parameters). Therefore, each individual
> > +test execution holds a pointer to this parent, accessible via a field named
> > +``parent``.
> > +
> > +It's possible to add resources to share between the individual test executions
> > +within a parameterized test series by using the ``KUNIT_CASE_PARAM_WITH_INIT``
> > +macro, to which you pass custom ``param_init`` and ``param_exit`` functions.
> > +These functions run once before and once after the entire parameterized test
> > +series, respectively. The ``param_init`` function can be used for adding any
> > +resources to the resources field of a parent test and also provide an additional
> > +way of setting the parameter array. The ``param_exit`` function can be used
> > +release any resources that were not test managed i.e. not automatically cleaned
> > +up after the test ends.
> > +
> > +.. note::
> > +   If both a ``generate_params`` function is passed to ``KUNIT_CASE_PARAM_WITH_INIT``
> > +   and an array is registered via ``kunit_register_params_array`` in
> > +   ``param_init``, the ``generate_params`` function will be used to get
> > +   the parameters.
>
> Maybe note that the ``generate_params`` function can use the array
> passed, though?

Will make this edit in v2

>
> > +
> > +Both ``param_init`` and ``param_exit`` are passed the parent instance of a test
> > +(parent ``struct kunit``) behind the scenes. However, the test case function
> > +receives the individual instance of a test for each parameter. Therefore, to
> > +manage and access shared resources from within a test case function, you must use
> > +``test->parent``.
> > +
> > +.. note::
> > +   The ``suite->init()`` function, which runs before each parameter execution,
> > +   receives the individual instance of a test for each parameter. Therefore,
> > +   resources set up in ``suite->init()`` are reset for each individual
> > +   parameterized test execution and are only visible within that specific test.
> > +
> > +For instance, finding a shared resource allocated by the Resource API requires
> > +passing ``test->parent`` to ``kunit_find_resource()``. This principle extends to
> > +all other APIs that might be used in the test case function, including
> > +``kunit_kzalloc()``, ``kunit_kmalloc_array()``, and others (see
> > +Documentation/dev-tools/kunit/api/test.rst and the
> > +Documentation/dev-tools/kunit/api/resource.rst).
> > +
> > +The code below shows how you can add the shared resources. Note that this code
> > +utilizes the Resource API, which you can read more about here:
> > +Documentation/dev-tools/kunit/api/resource.rst.
> > +
> > +.. code-block:: c
> > +
> > +       /* An example parameter array. */
> > +       static const struct example_param {
> > +               int value;
> > +       } example_params_array[] = {
> > +               { .value = 3, },
> > +               { .value = 2, },
> > +               { .value = 1, },
> > +               { .value = 0, },
> > +       };
> > +
> > +       /*
> > +        * This custom function allocates memory for the kunit_resource data field.
> > +        * The function is passed to kunit_alloc_resource() and executed once
> > +        * by the internal helper __kunit_add_resource().
> > +        */
> > +       static int example_resource_init(struct kunit_resource *res, void *context)
> > +       {
> > +               int *info = kmalloc(sizeof(*info), GFP_KERNEL);
> > +
> > +               if (!info)
> > +                       return -ENOMEM;
> > +               *info = *(int *)context;
> > +               res->data = info;
> > +               return 0;
> > +       }
> > +
> > +       /*
> > +        * This function deallocates memory for the 'kunit_resource' data field.
> > +        * The function is passed to kunit_alloc_resource() and automatically
> > +        * executes within kunit_release_resource() when the resource's reference
> > +        * count, via kunit_put_resource(), drops to zero. KUnit uses reference
> > +        * counting to ensure that resources are not freed prematurely.
> > +        */
> > +       static void example_resource_free(struct kunit_resource *res)
> > +       {
> > +               kfree(res->data);
> > +       }
> > +
> > +       /*
> > +        * This match function is invoked by kunit_find_resource() to locate
> > +        * a test resource based on defined criteria. The current example
> > +        * uniquely identifies the resource by its free function; however,
> > +        * alternative custom criteria can be implemented. Refer to
> > +        * lib/kunit/platform.c and lib/kunit/static_stub.c for further examples.
> > +        */
> > +       static bool example_resource_alloc_match(struct kunit *test,
> > +                                                struct kunit_resource *res,
> > +                                                void *match_data)
> > +       {
> > +               return res->data && res->free == example_resource_free;
> > +       }
> > +
> > +       /*
> > +        * This is an example of a function that provides a description for each of the
> > +        * parameters.
> > +       */
> > +       static void example_param_array_get_desc(const void *p, char *desc)
> > +       {
> > +               const struct example_param *param = p;
> > +
> > +               snprintf(desc, KUNIT_PARAM_DESC_SIZE,
> > +                       "example check if %d is less than or equal to 3", param->value);
> > +       }
> > +
> > +       /*
> > +        * Initializes the parent kunit struct for parameterized KUnit tests.
> > +        * This function enables sharing resources across all parameterized
> > +        * tests by adding them to the `parent` kunit test struct. It also supports
> > +        * registering either static or dynamic arrays of test parameters.
> > +        */
> > +       static int example_param_init(struct kunit *test)
> > +       {
> > +               int ctx = 3; /* Data to be stored. */
> > +               int arr_size = ARRAY_SIZE(example_params_array);
> > +
> > +               /*
> > +                * This allocates a struct kunit_resource, sets its data field to
> > +                * ctx, and adds it to the kunit struct's resources list. Note that
> > +                * this is test managed so we don't need to have a custom exit function
> > +                * to free it.
> > +                */
> > +               void *data = kunit_alloc_resource(test, example_resource_init, example_resource_free,
> > +                                                 GFP_KERNEL, &ctx);
> > +
> > +               if (!data)
> > +                       return -ENOMEM;
> > +               /* Pass the static param array information to the parent struct kunit. */
> > +               kunit_register_params_array(test, example_params_array, arr_size,
> > +                                           example_param_array_get_desc);
> > +               return 0;
> > +       }
> > +
> > +       /*
> > +       * This is an example of a parameterized test that uses shared resources
> > +       * available from the struct kunit parent field of the kunit struct.
> > +       */
> > +       static void example_params_test_with_init(struct kunit *test)
> > +       {
> > +               int threshold;
> > +               struct kunit_resource *res;
> > +               const struct example_param *param = test->param_value;
> > +
> > +               /* By design, param pointer will not be NULL. */
> > +               KUNIT_ASSERT_NOT_NULL(test, param);
> > +
> > +               /* Here we need to access the parent pointer of the test to find the shared resource. */
> > +               res = kunit_find_resource(test->parent, example_resource_alloc_match, NULL);
> > +
> > +               KUNIT_ASSERT_NOT_NULL(test, res);
> > +
> > +               /* Since the data field in kunit_resource is a void pointer we need to typecast it. */
> > +               threshold = *((int *)res->data);
> > +
> > +               /* Assert that the parameter is less than or equal to a certain threshold. */
> > +               KUNIT_ASSERT_LE(test, param->value, threshold);
> > +
> > +               /* This decreases the reference count after calling kunit_find_resource(). */
> > +               kunit_put_resource(res);
> > +       }
> > +
> > +
> > +       static struct kunit_case example_tests[] = {
> > +               KUNIT_CASE_PARAM_WITH_INIT(example_params_test_with_init, NULL,
> > +                                          example_param_init, NULL),
> > +               {}
> > +       };
> > +
>
> This is a really long example, which already exists in
> kunit-example-test.c. Can we either link to it there (and just include
> the most critical lines here), or have a smaller, less-complete
> example inline here?

Yes, I will do that in v2.

>
>
> > +As an alternative to using the KUnit Resource API for shared resources, you can
> > +place them in ``test->parent->priv``. It can store data that needs to persist
> > +and be accessible across all executions within a parameterized test series.
> > +
> > +As stated previously ``param_init`` and ``param_exit`` receive the parent
> > +``struct kunit`` instance. So, you can directly use ``test->priv`` within them
> > +to manage shared resources. However, from within the test case function, you must
> > +navigate up to the parent i.e. use ``test->parent->priv`` to access those same
> > +resources.
> > +
> > +The resources placed in ``test->parent-priv`` will also need to be allocated in
> > +memory to persist across the parameterized tests executions. If memory is
>
> Nit: 'parameterized test executions' singular?

Thank you for catching this! Though I will be changing all references to
parameter executions to "parameter runs" to be consistent with the
terminology in v2.

>
> > +allocated using the memory allocation APIs provided by KUnit (described more in
> > +the section below), you will not need to worry about deallocating them as they
> > +will be managed by the parent parameterized test that gets automatically cleaned
> > +up upon the end of the parameterized test series.
> > +
> > +The code below demonstrates example usage of the ``priv`` field for shared
> > +resources:
> > +
> > +.. code-block:: c
> > +
> > +       /* An example parameter array. */
> > +       static const struct example_param {
> > +               int value;
> > +       } example_params_array[] = {
> > +               { .value = 3, },
> > +               { .value = 2, },
> > +               { .value = 1, },
> > +               { .value = 0, },
> > +       };
> > +
> > +       /*
> > +        * Initializes the parent kunit struct for parameterized KUnit tests.
> > +        * This function enables sharing resources across all parameterized
> > +        * tests.
> > +        */
> > +       static int example_param_init_priv(struct kunit *test)
> > +       {
> > +               int ctx = 3; /* Data to be stored. */
> > +               int arr_size = ARRAY_SIZE(example_params_array);
> > +
> > +               /*
> > +                * Allocate memory using kunit_kzalloc(). Since the `param_init`
> > +                * function receives the parent instance of test, this memory
> > +                * allocation will be scoped to the lifetime of the whole
> > +                * parameterized test series.
> > +                */
> > +               test->priv = kunit_kzalloc(test, sizeof(int), GFP_KERNEL);
> > +
> > +               /* Assign the context value to test->priv.*/
> > +               *((int *)test->priv) = ctx;
> > +
> > +               /* Pass the static param array information to the parent struct kunit. */
> > +               kunit_register_params_array(test, example_params_array, arr_size, NULL);
> > +               return 0;
> > +       }
> > +
> > +       /*
> > +       * This is an example of a parameterized test that uses shared resources
> > +       * available from the struct kunit parent field of the kunit struct.
> > +       */
> > +       static void example_params_test_with_init_priv(struct kunit *test)
> > +       {
> > +               int threshold;
> > +               const struct example_param *param = test->param_value;
> > +
> > +               /* By design, param pointer will not be NULL. */
> > +               KUNIT_ASSERT_NOT_NULL(test, param);
> > +
> > +               /* By design, test->parent will also not be NULL. */
> > +               KUNIT_ASSERT_NOT_NULL(test, test->parent);
> > +
> > +               /* Assert that test->parent->priv has data. */
> > +               KUNIT_ASSERT_NOT_NULL(test, test->parent->priv);
> > +
> > +               /* Here we need to use test->parent->priv to access the shared resource. */
> > +               threshold = *(int *)test->parent->priv;
> > +
> > +               /* Assert that the parameter is less than or equal to a certain threshold. */
> > +               KUNIT_ASSERT_LE(test, param->value, threshold);
> > +       }
> > +
> > +
> > +       static struct kunit_case example_tests[] = {
> > +               KUNIT_CASE_PARAM_WITH_INIT(example_params_test_with_init_priv, NULL,
> > +                                          example_param_init_priv, NULL),
> > +               {}
> > +       };
> > +
>
> Again, this is a little long, but it's not as bad as the others, and
> isn't in the example tests, so I'm okay with leaving it. Though maybe
> we could get rid of some of the asserts for the purpose of keeping the
> documentation focused and readable.

Sounds good!


>
>
> >  Allocating Memory
> >  -----------------
> >
> > --
> > 2.50.1.552.g942d659e1b-goog
> >