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diff --git a/Documentation/dev-tools/kunit/usage.rst b/Documentation/dev-tools/kunit/usage.rst index 76af931a332c..ebd06f5ea455 100644 --- a/Documentation/dev-tools/kunit/usage.rst +++ b/Documentation/dev-tools/kunit/usage.rst @@ -112,11 +112,51 @@ terminates the test case if the condition is not satisfied. For example: KUNIT_EXPECT_LE(test, a[i], a[i + 1]); } -In this example, the method under test should return pointer to a value. If the -pointer returns null or an errno, we want to stop the test since the following -expectation could crash the test case. `ASSERT_NOT_ERR_OR_NULL(...)` allows us -to bail out of the test case if the appropriate conditions are not satisfied to -complete the test. +In this example, we need to be able to allocate an array to test the ``sort()`` +function. So we use ``KUNIT_ASSERT_NOT_ERR_OR_NULL()`` to abort the test if +there's an allocation error. + +.. note:: + In other test frameworks, ``ASSERT`` macros are often implemented by calling + ``return`` so they only work from the test function. In KUnit, we stop the + current kthread on failure, so you can call them from anywhere. + +.. note:: + Warning: There is an exception to the above rule. You shouldn't use assertions + in the suite's exit() function, or in the free function for a resource. These + run when a test is shutting down, and an assertion here prevents further + cleanup code from running, potentially leading to a memory leak. + +Customizing error messages +-------------------------- + +Each of the ``KUNIT_EXPECT`` and ``KUNIT_ASSERT`` macros have a ``_MSG`` +variant. These take a format string and arguments to provide additional +context to the automatically generated error messages. + +.. code-block:: c + + char some_str[41]; + generate_sha1_hex_string(some_str); + + /* Before. Not easy to tell why the test failed. */ + KUNIT_EXPECT_EQ(test, strlen(some_str), 40); + + /* After. Now we see the offending string. */ + KUNIT_EXPECT_EQ_MSG(test, strlen(some_str), 40, "some_str='%s'", some_str); + +Alternatively, one can take full control over the error message by using +``KUNIT_FAIL()``, e.g. + +.. code-block:: c + + /* Before */ + KUNIT_EXPECT_EQ(test, some_setup_function(), 0); + + /* After: full control over the failure message. */ + if (some_setup_function()) + KUNIT_FAIL(test, "Failed to setup thing for testing"); + Test Suites ~~~~~~~~~~~ @@ -125,8 +165,13 @@ We need many test cases covering all the unit's behaviors. It is common to have many similar tests. In order to reduce duplication in these closely related tests, most unit testing frameworks (including KUnit) provide the concept of a *test suite*. A test suite is a collection of test cases for a unit of code -with a setup function that gets invoked before every test case and then a tear -down function that gets invoked after every test case completes. For example: +with optional setup and teardown functions that run before/after the whole +suite and/or every test case. + +.. note:: + A test case will only run if it is associated with a test suite. + +For example: .. code-block:: c @@ -141,19 +186,25 @@ down function that gets invoked after every test case completes. For example: .name = "example", .init = example_test_init, .exit = example_test_exit, + .suite_init = example_suite_init, + .suite_exit = example_suite_exit, .test_cases = example_test_cases, }; kunit_test_suite(example_test_suite); -In the above example, the test suite ``example_test_suite`` would run the test -cases ``example_test_foo``, ``example_test_bar``, and ``example_test_baz``. Each -would have ``example_test_init`` called immediately before it and -``example_test_exit`` called immediately after it. -``kunit_test_suite(example_test_suite)`` registers the test suite with the -KUnit test framework. +In the above example, the test suite ``example_test_suite`` would first run +``example_suite_init``, then run the test cases ``example_test_foo``, +``example_test_bar``, and ``example_test_baz``. Each would have +``example_test_init`` called immediately before it and ``example_test_exit`` +called immediately after it. Finally, ``example_suite_exit`` would be called +after everything else. ``kunit_test_suite(example_test_suite)`` registers the +test suite with the KUnit test framework. .. note:: - A test case will only run if it is associated with a test suite. + The ``exit`` and ``suite_exit`` functions will run even if ``init`` or + ``suite_init`` fail. Make sure that they can handle any inconsistent + state which may result from ``init`` or ``suite_init`` encountering errors + or exiting early. ``kunit_test_suite(...)`` is a macro which tells the linker to put the specified test suite in a special linker section so that it can be run by KUnit @@ -162,6 +213,8 @@ built as a module). For more information, see Documentation/dev-tools/kunit/api/test.rst. +.. _kunit-on-non-uml: + Writing Tests For Other Architectures ------------------------------------- @@ -242,7 +295,7 @@ example: int rectangle_area(struct shape *this) { - struct rectangle *self = container_of(this, struct shape, parent); + struct rectangle *self = container_of(this, struct rectangle, parent); return self->length * self->width; }; @@ -489,11 +542,31 @@ 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. +To run a test case against multiple inputs, KUnit provides a parameterized +testing framework. This feature formalizes and extends the concept of +table-driven tests discussed previously. + +A KUnit test is determined to be parameterized if a parameter generator function +is provided when registering the test case. A test user can either write their +own generator function or use one that is provided by KUnit. The generator +function is stored in ``kunit_case->generate_params`` and can be set using the +macros described in the section below. + +To establish the terminology, a "parameterized test" is a test which is run +multiple times (once per "parameter" or "parameter run"). Each parameter run has +both its own independent ``struct kunit`` (the "parameter run context") and +access to a shared parent ``struct kunit`` (the "parameterized test context"). + +Passing Parameters to a Test +^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +There are three ways to provide the parameters to a test: + +Array Parameter Macros: -By reusing the same ``cases`` array from above, we can write the test as a -"parameterized test" with the following. + 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 @@ -502,7 +575,7 @@ By reusing the same ``cases`` array from above, we can write the test as a const char *str; const char *sha1; }; - struct sha1_test_case cases[] = { + static const struct sha1_test_case cases[] = { { .str = "hello world", .sha1 = "2aae6c35c94fcfb415dbe95f408b9ce91ee846ed", @@ -513,13 +586,9 @@ By reusing the same ``cases`` array from above, we can write the test as a }, }; - // Need a helper function to generate a name for each test case. - static void case_to_desc(const struct sha1_test_case *t, char *desc) - { - strcpy(desc, t->str); - } - // Creates `sha1_gen_params()` to iterate over `cases`. - KUNIT_ARRAY_PARAM(sha1, cases, case_to_desc); + // Creates `sha1_gen_params()` to iterate over `cases` while using + // the struct member `str` for the case description. + KUNIT_ARRAY_PARAM_DESC(sha1, cases, str); // Looks no different from a normal test. static void sha1_test(struct kunit *test) @@ -535,32 +604,324 @@ By reusing the same ``cases`` array from above, we can write the test as a } // Instead of KUNIT_CASE, we use KUNIT_CASE_PARAM and pass in the - // function declared by KUNIT_ARRAY_PARAM. + // function declared by KUNIT_ARRAY_PARAM or KUNIT_ARRAY_PARAM_DESC. static struct kunit_case sha1_test_cases[] = { KUNIT_CASE_PARAM(sha1_test, sha1_gen_params), {} }; -.. _kunit-on-non-uml: +Custom Parameter Generator Function: + + The generator function is responsible for generating parameters one-by-one + and has the following signature: + ``const void* (*)(struct kunit *test, const void *prev, char *desc)``. + You can pass the generator function to the ``KUNIT_CASE_PARAM`` + or ``KUNIT_CASE_PARAM_WITH_INIT`` macros. + + The function receives the previously generated parameter as the ``prev`` argument + (which is ``NULL`` on the first call) and can also access the parameterized + test context passed as the ``test`` argument. KUnit calls this function + repeatedly until it returns ``NULL``, which signifies that a parameterized + test ended. + + 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 run managed," meaning it's automatically cleaned up at + // the end of each parameter run. + 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), + {} + }; + +Runtime Parameter Array Registration in the Init Function: + + For scenarios where you might need to initialize a parameterized test, you + can directly register a parameter array to the parameterized test context. + + To do this, you must pass the parameterized test context, the array itself, + the array size, and a ``get_description()`` function to the + ``kunit_register_params_array()`` macro. This macro populates + ``struct kunit_params`` within the parameterized test context, effectively + storing a parameter array object. The ``get_description()`` function will + be used for populating parameter descriptions and has the following signature: + ``void (*)(struct kunit *test, const void *param, char *desc)``. Note that it + also has access to the parameterized test context. + + .. important:: + When using this way to register a parameter array, you will need to + manually pass ``kunit_array_gen_params()`` as the generator function to + ``KUNIT_CASE_PARAM_WITH_INIT``. ``kunit_array_gen_params()`` is a KUnit + helper that will use the registered array to generate the parameters. + + If needed, instead of passing the KUnit helper, you can also pass your + own custom generator function that utilizes the parameter array. To + access the parameter array from within the parameter generator + function use ``test->params_array.params``. + + The ``kunit_register_params_array()`` macro should be called within a + ``param_init()`` function that initializes the parameterized test and has + the following signature ``int (*)(struct kunit *test)``. For a detailed + explanation of this mechanism please refer to the "Adding Shared Resources" + section that is after this one. This method supports registering both + dynamically built and static parameter arrays. + + The code snippet below shows the ``example_param_init_dynamic_arr`` test that + utilizes ``make_fibonacci_params()`` to create a dynamic array, which is then + registered using ``kunit_register_params_array()``. To see the full code + please refer to lib/kunit/kunit-example-test.c. + +.. code-block:: c + + /* + * Example of a parameterized test param_init() function that registers a dynamic + * array of parameters. + */ + static int example_param_init_dynamic_arr(struct kunit *test) + { + size_t seq_size; + int *fibonacci_params; + + kunit_info(test, "initializing parameterized test\n"); + + seq_size = 6; + fibonacci_params = make_fibonacci_params(test, seq_size); + if (!fibonacci_params) + return -ENOMEM; + /* + * Passes the dynamic parameter array information to the parameterized test + * context struct kunit. The array and its metadata will be stored in + * test->parent->params_array. 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; + } + + static struct kunit_case example_test_cases[] = { + /* + * Note how we pass kunit_array_gen_params() to use the array we + * registered in example_param_init_dynamic_arr() to generate + * parameters. + */ + KUNIT_CASE_PARAM_WITH_INIT(example_params_test_with_init_dynamic_arr, + kunit_array_gen_params, + example_param_init_dynamic_arr, + example_param_exit_dynamic_arr), + {} + }; + +Adding Shared Resources +^^^^^^^^^^^^^^^^^^^^^^^ +All parameter runs in this framework hold a reference to the parameterized test +context, which can be accessed using the parent ``struct kunit`` pointer. The +parameterized test context is not used to execute any test logic itself; instead, +it serves as a container for shared resources. + +It's possible to add resources to share between parameter runs within a +parameterized test by using ``KUNIT_CASE_PARAM_WITH_INIT``, to which you pass +custom ``param_init()`` and ``param_exit()`` functions. These functions run once +before and once after the parameterized test, respectively. + +The ``param_init()`` function, with the signature ``int (*)(struct kunit *test)``, +can be used for adding resources to the ``resources`` or ``priv`` fields of +the parameterized test context, registering the parameter array, and any other +initialization logic. + +The ``param_exit()`` function, with the signature ``void (*)(struct kunit *test)``, +can be used to release any resources that were not parameterized test managed (i.e. +not automatically cleaned up after the parameterized test ends) and for any other +exit logic. + +Both ``param_init()`` and ``param_exit()`` are passed the parameterized test +context behind the scenes. However, the test case function receives the parameter +run context. Therefore, to manage and access shared resources from within a test +case function, you must use ``test->parent``. + +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). + +.. note:: + The ``suite->init()`` function, which executes before each parameter run, + receives the parameter run context. Therefore, any resources set up in + ``suite->init()`` are cleaned up after each parameter run. + +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. To see the full version of this +code please refer to lib/kunit/kunit-example-test.c. + +.. code-block:: c + + static int example_resource_init(struct kunit_resource *res, void *context) + { + ... /* Code that allocates memory and stores context in res->data. */ + } + + /* This function deallocates memory for the kunit_resource->data field. */ + static void example_resource_free(struct kunit_resource *res) + { + kfree(res->data); + } + + /* This match function locates a test resource based on defined criteria. */ + static bool example_resource_alloc_match(struct kunit *test, struct kunit_resource *res, + void *match_data) + { + return res->data && res->free == example_resource_free; + } + + /* Function to initialize the parameterized test. */ + static int example_param_init(struct kunit *test) + { + int ctx = 3; /* Data to be stored. */ + void *data = kunit_alloc_resource(test, example_resource_init, + example_resource_free, + GFP_KERNEL, &ctx); + if (!data) + return -ENOMEM; + kunit_register_params_array(test, example_params_array, + ARRAY_SIZE(example_params_array)); + return 0; + } + + /* Example test that uses shared resources in test->resources. */ + static void example_params_test_with_init(struct kunit *test) + { + int threshold; + const struct example_param *param = test->param_value; + /* Here we pass test->parent to access the parameterized test context. */ + struct kunit_resource *res = kunit_find_resource(test->parent, + example_resource_alloc_match, + NULL); + + threshold = *((int *)res->data); + KUNIT_ASSERT_LE(test, param->value, threshold); + kunit_put_resource(res); + } + + static struct kunit_case example_test_cases[] = { + KUNIT_CASE_PARAM_WITH_INIT(example_params_test_with_init, kunit_array_gen_params, + example_param_init, NULL), + {} + }; -Exiting Early on Failed Expectations ------------------------------------- +As an alternative to using the KUnit Resource API for sharing resources, you can +place them in ``test->parent->priv``. This serves as a more lightweight method +for resource storage, best for scenarios where complex resource management is +not required. -We can use ``KUNIT_EXPECT_EQ`` to mark the test as failed and continue -execution. In some cases, it is unsafe to continue. We can use the -``KUNIT_ASSERT`` variant to exit on failure. +As stated previously ``param_init()`` and ``param_exit()`` get the parameterized +test context. So, you can directly use ``test->priv`` within ``param_init/exit`` +to manage shared resources. However, from within the test case function, you must +navigate up to the parent ``struct kunit`` i.e. the parameterized test context. +Therefore, you need to use ``test->parent->priv`` to access those same +resources. + +The resources placed in ``test->parent->priv`` will need to be allocated in +memory to persist across the parameter runs. If memory is allocated using the +KUnit memory allocation APIs (described more in the "Allocating Memory" section +below), you won't need to worry about deallocation. The APIs will make the memory +parameterized test 'managed', ensuring that it will automatically get cleaned up +after the parameterized test concludes. + +The code below demonstrates example usage of the ``priv`` field for shared +resources: .. code-block:: c - void example_test_user_alloc_function(struct kunit *test) + static const struct example_param { + int value; + } example_params_array[] = { + { .value = 3, }, + { .value = 2, }, + { .value = 1, }, + { .value = 0, }, + }; + + /* Initialize the parameterized test context. */ + 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 parameterized test context, this memory + * allocation will be scoped to the lifetime of the parameterized test. + */ + test->priv = kunit_kzalloc(test, sizeof(int), GFP_KERNEL); + + /* Assign the context value to test->priv.*/ + *((int *)test->priv) = ctx; + + /* Register the parameter array. */ + kunit_register_params_array(test, example_params_array, arr_size, NULL); + return 0; + } + + static void example_params_test_with_init_priv(struct kunit *test) { - void *object = alloc_some_object_for_me(); + int threshold; + const struct example_param *param = test->param_value; + + /* By design, test->parent will not be NULL. */ + KUNIT_ASSERT_NOT_NULL(test, test->parent); + + /* Here we use test->parent->priv to access the shared resource. */ + threshold = *(int *)test->parent->priv; - /* Make sure we got a valid pointer back. */ - KUNIT_ASSERT_NOT_ERR_OR_NULL(test, object); - do_something_with_object(object); + KUNIT_ASSERT_LE(test, param->value, threshold); } + static struct kunit_case example_tests[] = { + KUNIT_CASE_PARAM_WITH_INIT(example_params_test_with_init_priv, + kunit_array_gen_params, + example_param_init_priv, NULL), + {} + }; + Allocating Memory ----------------- @@ -582,17 +943,109 @@ For example: KUNIT_ASSERT_STREQ(test, buffer, ""); } +Registering Cleanup Actions +--------------------------- + +If you need to perform some cleanup beyond simple use of ``kunit_kzalloc``, +you can register a custom "deferred action", which is a cleanup function +run when the test exits (whether cleanly, or via a failed assertion). + +Actions are simple functions with no return value, and a single ``void*`` +context argument, and fulfill the same role as "cleanup" functions in Python +and Go tests, "defer" statements in languages which support them, and +(in some cases) destructors in RAII languages. + +These are very useful for unregistering things from global lists, closing +files or other resources, or freeing resources. + +For example: + +.. code-block:: C + + static void cleanup_device(void *ctx) + { + struct device *dev = (struct device *)ctx; + + device_unregister(dev); + } + + void example_device_test(struct kunit *test) + { + struct my_device dev; + + device_register(&dev); + + kunit_add_action(test, &cleanup_device, &dev); + } + +Note that, for functions like device_unregister which only accept a single +pointer-sized argument, it's possible to automatically generate a wrapper +with the ``KUNIT_DEFINE_ACTION_WRAPPER()`` macro, for example: + +.. code-block:: C + + KUNIT_DEFINE_ACTION_WRAPPER(device_unregister, device_unregister_wrapper, struct device *); + kunit_add_action(test, &device_unregister_wrapper, &dev); + +You should do this in preference to manually casting to the ``kunit_action_t`` type, +as casting function pointers will break Control Flow Integrity (CFI). + +``kunit_add_action`` can fail if, for example, the system is out of memory. +You can use ``kunit_add_action_or_reset`` instead which runs the action +immediately if it cannot be deferred. + +If you need more control over when the cleanup function is called, you +can trigger it early using ``kunit_release_action``, or cancel it entirely +with ``kunit_remove_action``. + Testing Static Functions ------------------------ -If we do not want to expose functions or variables for testing, one option is to -conditionally ``#include`` the test file at the end of your .c file. For -example: +If you want to test static functions without exposing those functions outside of +testing, one option is conditionally export the symbol. When KUnit is enabled, +the symbol is exposed but remains static otherwise. To use this method, follow +the template below. .. code-block:: c - /* In my_file.c */ + /* In the file containing functions to test "my_file.c" */ + + #include <kunit/visibility.h> + #include <my_file.h> + ... + VISIBLE_IF_KUNIT int do_interesting_thing() + { + ... + } + EXPORT_SYMBOL_IF_KUNIT(do_interesting_thing); + + /* In the header file "my_file.h" */ + + #if IS_ENABLED(CONFIG_KUNIT) + int do_interesting_thing(void); + #endif + + /* In the KUnit test file "my_file_test.c" */ + + #include <kunit/visibility.h> + #include <my_file.h> + ... + MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING"); + ... + // Use do_interesting_thing() in tests + +For a full example, see this `patch <https://lore.kernel.org/all/20221207014024.340230-3-rmoar@google.com/>`_ +where a test is modified to conditionally expose static functions for testing +using the macros above. + +As an **alternative** to the method above, you could conditionally ``#include`` +the test file at the end of your .c file. This is not recommended but works +if needed. For example: + +.. code-block:: c + + /* In "my_file.c" */ static int do_interesting_thing(); @@ -622,17 +1075,22 @@ as shown in next section: *Accessing The Current Test*. Accessing The Current Test -------------------------- -In some cases, we need to call test-only code from outside the test file. -For example, see example in section *Injecting Test-Only Code* or if -we are providing a fake implementation of an ops struct. Using -``kunit_test`` field in ``task_struct``, we can access it via -``current->kunit_test``. +In some cases, we need to call test-only code from outside the test file. This +is helpful, for example, when providing a fake implementation of a function, or +to fail any current test from within an error handler. +We can do this via the ``kunit_test`` field in ``task_struct``, which we can +access using the ``kunit_get_current_test()`` function in ``kunit/test-bug.h``. + +``kunit_get_current_test()`` is safe to call even if KUnit is not enabled. If +KUnit is not enabled, or if no test is running in the current task, it will +return ``NULL``. This compiles down to either a no-op or a static key check, +so will have a negligible performance impact when no test is running. -The example below includes how to implement "mocking": +The example below uses this to implement a "mock" implementation of a function, ``foo``: .. code-block:: c - #include <linux/sched.h> /* for current */ + #include <kunit/test-bug.h> /* for kunit_get_current_test */ struct test_data { int foo_result; @@ -641,7 +1099,7 @@ The example below includes how to implement "mocking": static int fake_foo(int arg) { - struct kunit *test = current->kunit_test; + struct kunit *test = kunit_get_current_test(); struct test_data *test_data = test->priv; KUNIT_EXPECT_EQ(test, test_data->want_foo_called_with, arg); @@ -672,7 +1130,7 @@ Each test can have multiple resources which have string names providing the same flexibility as a ``priv`` member, but also, for example, allowing helper functions to create resources without conflicting with each other. It is also possible to define a clean up function for each resource, making it easy to -avoid resource leaks. For more information, see Documentation/dev-tools/kunit/api/test.rst. +avoid resource leaks. For more information, see Documentation/dev-tools/kunit/api/resource.rst. Failing The Current Test ------------------------ @@ -700,3 +1158,57 @@ structures as shown below: static void my_debug_function(void) { } #endif +``kunit_fail_current_test()`` is safe to call even if KUnit is not enabled. If +KUnit is not enabled, or if no test is running in the current task, it will do +nothing. This compiles down to either a no-op or a static key check, so will +have a negligible performance impact when no test is running. + +Managing Fake Devices and Drivers +--------------------------------- + +When testing drivers or code which interacts with drivers, many functions will +require a ``struct device`` or ``struct device_driver``. In many cases, setting +up a real device is not required to test any given function, so a fake device +can be used instead. + +KUnit provides helper functions to create and manage these fake devices, which +are internally of type ``struct kunit_device``, and are attached to a special +``kunit_bus``. These devices support managed device resources (devres), as +described in Documentation/driver-api/driver-model/devres.rst + +To create a KUnit-managed ``struct device_driver``, use ``kunit_driver_create()``, +which will create a driver with the given name, on the ``kunit_bus``. This driver +will automatically be destroyed when the corresponding test finishes, but can also +be manually destroyed with ``driver_unregister()``. + +To create a fake device, use the ``kunit_device_register()``, which will create +and register a device, using a new KUnit-managed driver created with ``kunit_driver_create()``. +To provide a specific, non-KUnit-managed driver, use ``kunit_device_register_with_driver()`` +instead. Like with managed drivers, KUnit-managed fake devices are automatically +cleaned up when the test finishes, but can be manually cleaned up early with +``kunit_device_unregister()``. + +The KUnit devices should be used in preference to ``root_device_register()``, and +instead of ``platform_device_register()`` in cases where the device is not otherwise +a platform device. + +For example: + +.. code-block:: c + + #include <kunit/device.h> + + static void test_my_device(struct kunit *test) + { + struct device *fake_device; + const char *dev_managed_string; + + // Create a fake device. + fake_device = kunit_device_register(test, "my_device"); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, fake_device) + + // Pass it to functions which need a device. + dev_managed_string = devm_kstrdup(fake_device, "Hello, World!"); + + // Everything is cleaned up automatically when the test ends. + }
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