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Writing Tests=============
Test Cases----------
The fundamental unit in KUnit is the test case. A test case is a function withthe signature ``void (*)(struct kunit *test)``. It calls the function under testand then sets *expectations* for what should happen. For example:
.. code-block:: c
void example_test_success(struct kunit *test) { }
void example_test_failure(struct kunit *test) { KUNIT_FAIL(test, "This test never passes."); }
In the above example, ``example_test_success`` always passes because it doesnothing; no expectations are set, and therefore all expectations pass. On theother hand ``example_test_failure`` always fails because it calls ``KUNIT_FAIL``,which is a special expectation that logs a message and causes the test case tofail.
Expectations~~~~~~~~~~~~An *expectation* specifies that we expect a piece of code to do something in atest. An expectation is called like a function. A test is made by settingexpectations about the behavior of a piece of code under test. When one or moreexpectations fail, the test case fails and information about the failure islogged. For example:
.. code-block:: c
void add_test_basic(struct kunit *test) { KUNIT_EXPECT_EQ(test, 1, add(1, 0)); KUNIT_EXPECT_EQ(test, 2, add(1, 1)); }
In the above example, ``add_test_basic`` makes a number of assertions about thebehavior of a function called ``add``. The first parameter is always of type``struct kunit *``, which contains information about the current test context.The second parameter, in this case, is what the value is expected to be. Thelast value is what the value actually is. If ``add`` passes all of theseexpectations, the test case, ``add_test_basic`` will pass; if any one of theseexpectations fails, the test case will fail.
A test case *fails* when any expectation is violated; however, the test willcontinue to run, and try other expectations until the test case ends or isotherwise terminated. This is as opposed to *assertions* which are discussedlater.
To learn about more KUnit expectations, see Documentation/dev-tools/kunit/api/test.rst.
.. note:: A single test case should be short, easy to understand, and focused on a single behavior.
For example, if we want to rigorously test the ``add`` function above, createadditional tests cases which would test each property that an ``add`` functionshould have as shown below:
.. code-block:: c
void add_test_basic(struct kunit *test) { KUNIT_EXPECT_EQ(test, 1, add(1, 0)); KUNIT_EXPECT_EQ(test, 2, add(1, 1)); }
void add_test_negative(struct kunit *test) { KUNIT_EXPECT_EQ(test, 0, add(-1, 1)); }
void add_test_max(struct kunit *test) { KUNIT_EXPECT_EQ(test, INT_MAX, add(0, INT_MAX)); KUNIT_EXPECT_EQ(test, -1, add(INT_MAX, INT_MIN)); }
void add_test_overflow(struct kunit *test) { KUNIT_EXPECT_EQ(test, INT_MIN, add(INT_MAX, 1)); }
Assertions~~~~~~~~~~
An assertion is like an expectation, except that the assertion immediatelyterminates the test case if the condition is not satisfied. For example:
.. code-block:: c
static void test_sort(struct kunit *test) { int *a, i, r = 1; a = kunit_kmalloc_array(test, TEST_LEN, sizeof(*a), GFP_KERNEL); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, a); for (i = 0; i < TEST_LEN; i++) { r = (r * 725861) % 6599; a[i] = r; } sort(a, TEST_LEN, sizeof(*a), cmpint, NULL); for (i = 0; i < TEST_LEN-1; i++) KUNIT_EXPECT_LE(test, a[i], a[i + 1]); }
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 ifthere'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 additionalcontext 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");
Suppressing warning backtraces------------------------------
Some unit tests trigger warning backtraces either intentionally or as a sideeffect. Such backtraces are normally undesirable since they distract fromthe actual test and may result in the impression that there is a problem.
Backtraces can be suppressed with **task-scoped suppression**: whilesuppression is active on the current task, the backtrace and stack dump from``WARN*()``, ``WARN_ON*()``, and related macros on that task are suppressed.Two API forms are available.
- Scoped suppression is the simplest form. Wrap the code that triggers warnings in a ``kunit_warning_suppress()`` block:
.. code-block:: c
static void some_test(struct kunit *test) { kunit_warning_suppress(test) { trigger_backtrace(); KUNIT_EXPECT_SUPPRESSED_WARNING_COUNT(test, 1); } }
.. note:: The warning count must be checked inside the block; the suppression handle is not accessible after the block exits.
- Direct functions return an explicit handle pointer. Use them when the handle needs to be retained or passed across helper functions:
.. code-block:: c
static void some_test(struct kunit *test) { struct kunit_suppressed_warning *w;
w = kunit_start_suppress_warning(test); trigger_backtrace(); kunit_end_suppress_warning(test, w);
KUNIT_EXPECT_EQ(test, kunit_suppressed_warning_count(w), 1); }
Test Suites~~~~~~~~~~~
We need many test cases covering all the unit's behaviors. It is common to havemany similar tests. In order to reduce duplication in these closely relatedtests, 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 codewith optional setup and teardown functions that run before/after the wholesuite 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
static struct kunit_case example_test_cases[] = { KUNIT_CASE(example_test_foo), KUNIT_CASE(example_test_bar), KUNIT_CASE(example_test_baz), {} };
static struct kunit_suite example_test_suite = { .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 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 calledafter everything else. ``kunit_test_suite(example_test_suite)`` registers thetest suite with the KUnit test framework.
.. note:: 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 thespecified test suite in a special linker section so that it can be run by KUniteither after ``late_init``, or when the test module is loaded (if the test wasbuilt as a module).
For more information, see Documentation/dev-tools/kunit/api/test.rst.
.. _kunit-on-non-uml:
Writing Tests For Other Architectures-------------------------------------
It is better to write tests that run on UML to tests that only run under aparticular architecture. It is better to write tests that run under QEMU oranother easy to obtain (and monetarily free) software environment to a specificpiece of hardware.
Nevertheless, there are still valid reasons to write a test that is architectureor hardware specific. For example, we might want to test code that reallybelongs in ``arch/some-arch/*``. Even so, try to write the test so that it doesnot depend on physical hardware. Some of our test cases may not need hardware,only few tests actually require the hardware to test it. When hardware is notavailable, instead of disabling tests, we can skip them.
Now that we have narrowed down exactly what bits are hardware specific, theactual procedure for writing and running the tests is same as writing normalKUnit tests.
.. important:: We may have to reset hardware state. If this is not possible, we may only be able to run one test case per invocation.
.. TODO(brendanhiggins@google.com): Add an actual example of an architecture- dependent KUnit test.
Common Patterns===============
Isolating Behavior------------------
Unit testing limits the amount of code under test to a single unit. It controlswhat code gets run when the unit under test calls a function. Where a functionis exposed as part of an API such that the definition of that function can bechanged without affecting the rest of the code base. In the kernel, this comesfrom two constructs: classes, which are structs that contain function pointersprovided by the implementer, and architecture-specific functions, which havedefinitions selected at compile time.
Classes~~~~~~~
Classes are not a construct that is built into the C programming language;however, it is an easily derived concept. Accordingly, in most cases, everyproject that does not use a standardized object oriented library (like GNOME'sGObject) has their own slightly different way of doing object orientedprogramming; the Linux kernel is no exception.
The central concept in kernel object oriented programming is the class. In thekernel, a *class* is a struct that contains function pointers. This creates acontract between *implementers* and *users* since it forces them to use thesame function signature without having to call the function directly. To be aclass, the function pointers must specify that a pointer to the class, known asa *class handle*, be one of the parameters. Thus the member functions (alsoknown as *methods*) have access to member variables (also known as *fields*)allowing the same implementation to have multiple *instances*.
A class can be *overridden* by *child classes* by embedding the *parent class*in the child class. Then when the child class *method* is called, the childimplementation knows that the pointer passed to it is of a parent containedwithin the child. Thus, the child can compute the pointer to itself because thepointer to the parent is always a fixed offset from the pointer to the child.This offset is the offset of the parent contained in the child struct. Forexample:
.. code-block:: c
struct shape { int (*area)(struct shape *this); };
struct rectangle { struct shape parent; int length; int width; };
int rectangle_area(struct shape *this) { struct rectangle *self = container_of(this, struct rectangle, parent);
return self->length * self->width; };
void rectangle_new(struct rectangle *self, int length, int width) { self->parent.area = rectangle_area; self->length = length; self->width = width; }
In this example, computing the pointer to the child from the pointer to theparent is done by ``container_of``.
Faking Classes~~~~~~~~~~~~~~
In order to unit test a piece of code that calls a method in a class, thebehavior of the method must be controllable, otherwise the test ceases to be aunit test and becomes an integration test.
A fake class implements a piece of code that is different than what runs in aproduction instance, but behaves identical from the standpoint of the callers.This is done to replace a dependency that is hard to deal with, or is slow. Forexample, implementing a fake EEPROM that stores the "contents" in aninternal buffer. Assume we have a class that represents an EEPROM:
.. code-block:: c
struct eeprom { ssize_t (*read)(struct eeprom *this, size_t offset, char *buffer, size_t count); ssize_t (*write)(struct eeprom *this, size_t offset, const char *buffer, size_t count); };
And we want to test code that buffers writes to the EEPROM:
.. code-block:: c
struct eeprom_buffer { ssize_t (*write)(struct eeprom_buffer *this, const char *buffer, size_t count); int flush(struct eeprom_buffer *this); size_t flush_count; /* Flushes when buffer exceeds flush_count. */ };
struct eeprom_buffer *new_eeprom_buffer(struct eeprom *eeprom); void destroy_eeprom_buffer(struct eeprom *eeprom);
We can test this code by *faking out* the underlying EEPROM:
.. code-block:: c
struct fake_eeprom { struct eeprom parent; char contents[FAKE_EEPROM_CONTENTS_SIZE]; };
ssize_t fake_eeprom_read(struct eeprom *parent, size_t offset, char *buffer, size_t count) { struct fake_eeprom *this = container_of(parent, struct fake_eeprom, parent);
count = min(count, FAKE_EEPROM_CONTENTS_SIZE - offset); memcpy(buffer, this->contents + offset, count);
return count; }
ssize_t fake_eeprom_write(struct eeprom *parent, size_t offset, const char *buffer, size_t count) { struct fake_eeprom *this = container_of(parent, struct fake_eeprom, parent);
count = min(count, FAKE_EEPROM_CONTENTS_SIZE - offset); memcpy(this->contents + offset, buffer, count);
return count; }
void fake_eeprom_init(struct fake_eeprom *this) { this->parent.read = fake_eeprom_read; this->parent.write = fake_eeprom_write; memset(this->contents, 0, FAKE_EEPROM_CONTENTS_SIZE); }
We can now use it to test ``struct eeprom_buffer``:
.. code-block:: c
struct eeprom_buffer_test { struct fake_eeprom *fake_eeprom; struct eeprom_buffer *eeprom_buffer; };
static void eeprom_buffer_test_does_not_write_until_flush(struct kunit *test) { struct eeprom_buffer_test *ctx = test->priv; struct eeprom_buffer *eeprom_buffer = ctx->eeprom_buffer; struct fake_eeprom *fake_eeprom = ctx->fake_eeprom; char buffer[] = {0xff};
eeprom_buffer->flush_count = SIZE_MAX;
eeprom_buffer->write(eeprom_buffer, buffer, 1); KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0);
eeprom_buffer->write(eeprom_buffer, buffer, 1); KUNIT_EXPECT_EQ(test, fake_eeprom->contents[1], 0);
eeprom_buffer->flush(eeprom_buffer); KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0xff); KUNIT_EXPECT_EQ(test, fake_eeprom->contents[1], 0xff); }
static void eeprom_buffer_test_flushes_after_flush_count_met(struct kunit *test) { struct eeprom_buffer_test *ctx = test->priv; struct eeprom_buffer *eeprom_buffer = ctx->eeprom_buffer; struct fake_eeprom *fake_eeprom = ctx->fake_eeprom; char buffer[] = {0xff};
eeprom_buffer->flush_count = 2;
eeprom_buffer->write(eeprom_buffer, buffer, 1); KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0);
eeprom_buffer->write(eeprom_buffer, buffer, 1); KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0xff); KUNIT_EXPECT_EQ(test, fake_eeprom->contents[1], 0xff); }
static void eeprom_buffer_test_flushes_increments_of_flush_count(struct kunit *test) { struct eeprom_buffer_test *ctx = test->priv; struct eeprom_buffer *eeprom_buffer = ctx->eeprom_buffer; struct fake_eeprom *fake_eeprom = ctx->fake_eeprom; char buffer[] = {0xff, 0xff};
eeprom_buffer->flush_count = 2;
eeprom_buffer->write(eeprom_buffer, buffer, 1); KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0);
eeprom_buffer->write(eeprom_buffer, buffer, 2); KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0xff); KUNIT_EXPECT_EQ(test, fake_eeprom->contents[1], 0xff); /* Should have only flushed the first two bytes. */ KUNIT_EXPECT_EQ(test, fake_eeprom->contents[2], 0); }
static int eeprom_buffer_test_init(struct kunit *test) { struct eeprom_buffer_test *ctx;
ctx = kunit_kzalloc(test, sizeof(*ctx), GFP_KERNEL); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx);
ctx->fake_eeprom = kunit_kzalloc(test, sizeof(*ctx->fake_eeprom), GFP_KERNEL); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx->fake_eeprom); fake_eeprom_init(ctx->fake_eeprom);
ctx->eeprom_buffer = new_eeprom_buffer(&ctx->fake_eeprom->parent); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx->eeprom_buffer);
test->priv = ctx;
return 0; }
static void eeprom_buffer_test_exit(struct kunit *test) { struct eeprom_buffer_test *ctx = test->priv;
destroy_eeprom_buffer(ctx->eeprom_buffer); }
Testing Against Multiple Inputs-------------------------------
Testing just a few inputs is not enough to ensure that the code works correctly,for example: testing a hash function.
We can write a helper macro or function. The function is called for each input.For example, to test ``sha1sum(1)``, we can write:
.. code-block:: c
#define TEST_SHA1(in, want) \ sha1sum(in, out); \ KUNIT_EXPECT_STREQ_MSG(test, out, want, "sha1sum(%s)", in);
char out[40]; TEST_SHA1("hello world", "2aae6c35c94fcfb415dbe95f408b9ce91ee846ed"); TEST_SHA1("hello world!", "430ce34d020724ed75a196dfc2ad67c77772d169");
Note the use of the ``_MSG`` version of ``KUNIT_EXPECT_STREQ`` to print a moredetailed error and make the assertions clearer within the helper macros.
The ``_MSG`` variants are useful when the same expectation is called multipletimes (in a loop or helper function) and thus the line number is not enough toidentify what failed, as shown below.
In complicated cases, we recommend using a *table-driven test* compared to thehelper macro variation, for example:
.. code-block:: c
int i; char out[40];
struct sha1_test_case { const char *str; const char *sha1; };
struct sha1_test_case cases[] = { { .str = "hello world", .sha1 = "2aae6c35c94fcfb415dbe95f408b9ce91ee846ed", }, { .str = "hello world!", .sha1 = "430ce34d020724ed75a196dfc2ad67c77772d169", }, }; for (i = 0; i < ARRAY_SIZE(cases); ++i) { sha1sum(cases[i].str, out); KUNIT_EXPECT_STREQ_MSG(test, out, cases[i].sha1, "sha1sum(%s)", cases[i].str); }
There is more boilerplate code involved, but it can:
* be more readable when there are multiple inputs/outputs (due to field names).
* For example, see ``fs/ext4/inode-test.c``.
* reduce duplication if test cases are shared across multiple tests.
* For example: if we want to test ``sha256sum``, we could add a ``sha256`` field and reuse ``cases``.
* be converted to a "parameterized test".
Parameterized Testing~~~~~~~~~~~~~~~~~~~~~
To run a test case against multiple inputs, KUnit provides a parameterizedtesting framework. This feature formalizes and extends the concept oftable-driven tests discussed previously.
A KUnit test is determined to be parameterized if a parameter generator functionis provided when registering the test case. A test user can either write theirown generator function or use one that is provided by KUnit. The generatorfunction is stored in ``kunit_case->generate_params`` and can be set using themacros described in the section below.
To establish the terminology, a "parameterized test" is a test which is runmultiple times (once per "parameter" or "parameter run"). Each parameter run hasboth its own independent ``struct kunit`` (the "parameter run context") andaccess 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:
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
// This is copy-pasted from above. struct sha1_test_case { const char *str; const char *sha1; }; static const struct sha1_test_case cases[] = { { .str = "hello world", .sha1 = "2aae6c35c94fcfb415dbe95f408b9ce91ee846ed", }, { .str = "hello world!", .sha1 = "430ce34d020724ed75a196dfc2ad67c77772d169", }, };
// 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) { // This function can just contain the body of the for-loop. // The former `cases[i]` is accessible under test->param_value. char out[40]; struct sha1_test_case *test_param = (struct sha1_test_case *)(test->param_value);
sha1sum(test_param->str, out); KUNIT_EXPECT_STREQ_MSG(test, out, test_param->sha1, "sha1sum(%s)", test_param->str); }
// Instead of KUNIT_CASE, we use KUNIT_CASE_PARAM and pass in the // 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), {} };
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 testcontext, which can be accessed using the parent ``struct kunit`` pointer. Theparameterized 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 aparameterized test by using ``KUNIT_CASE_PARAM_WITH_INIT``, to which you passcustom ``param_init()`` and ``param_exit()`` functions. These functions run oncebefore 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 ofthe parameterized test context, registering the parameter array, and any otherinitialization 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 otherexit logic.
Both ``param_init()`` and ``param_exit()`` are passed the parameterized testcontext behind the scenes. However, the test case function receives the parameterrun context. Therefore, to manage and access shared resources from within a testcase function, you must use ``test->parent``.
For instance, finding a shared resource allocated by the Resource API requirespassing ``test->parent`` to ``kunit_find_resource()``. This principle extends toall other APIs that might be used in the test case function, including``kunit_kzalloc()``, ``kunit_kmalloc_array()``, and others (seeDocumentation/dev-tools/kunit/api/test.rst and theDocumentation/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 codeutilizes the Resource API, which you can read more about here:Documentation/dev-tools/kunit/api/resource.rst. To see the full version of thiscode 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), {} };
As an alternative to using the KUnit Resource API for sharing resources, you canplace them in ``test->parent->priv``. This serves as a more lightweight methodfor resource storage, best for scenarios where complex resource management isnot required.
As stated previously ``param_init()`` and ``param_exit()`` get the parameterizedtest context. So, you can directly use ``test->priv`` within ``param_init/exit``to manage shared resources. However, from within the test case function, you mustnavigate up to the parent ``struct kunit`` i.e. the parameterized test context.Therefore, you need to use ``test->parent->priv`` to access those sameresources.
The resources placed in ``test->parent->priv`` will need to be allocated inmemory to persist across the parameter runs. If memory is allocated using theKUnit memory allocation APIs (described more in the "Allocating Memory" sectionbelow), you won't need to worry about deallocation. The APIs will make the memoryparameterized test 'managed', ensuring that it will automatically get cleaned upafter the parameterized test concludes.
The code below demonstrates example usage of the ``priv`` field for sharedresources:
.. code-block:: c
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) { 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;
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-----------------
Where you might use ``kzalloc``, you can instead use ``kunit_kzalloc`` as KUnitwill then ensure that the memory is freed once the test completes.
This is useful because it lets us use the ``KUNIT_ASSERT_EQ`` macros to exitearly from a test without having to worry about remembering to call ``kfree``.For example:
.. code-block:: c
void example_test_allocation(struct kunit *test) { char *buffer = kunit_kzalloc(test, 16, GFP_KERNEL); /* Ensure allocation succeeded. */ KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buffer);
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 functionrun 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 Pythonand 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, closingfiles 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 singlepointer-sized argument, it's possible to automatically generate a wrapperwith 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 actionimmediately if it cannot be deferred.
If you need more control over when the cleanup function is called, youcan trigger it early using ``kunit_release_action``, or cancel it entirelywith ``kunit_remove_action``.
Testing Static Functions------------------------
If you want to test static functions without exposing those functions outside oftesting, one option is conditionally export the symbol. When KUnit is enabled,the symbol is exposed but remains static otherwise. To use this method, followthe template below.
.. code-block:: 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 testingusing 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 worksif needed. For example:
.. code-block:: c
/* In "my_file.c" */
static int do_interesting_thing();
#ifdef CONFIG_MY_KUNIT_TEST #include "my_kunit_test.c" #endif
Injecting Test-Only Code------------------------
Similar to as shown above, we can add test-specific logic. For example:
.. code-block:: c
/* In my_file.h */
#ifdef CONFIG_MY_KUNIT_TEST /* Defined in my_kunit_test.c */ void test_only_hook(void); #else void test_only_hook(void) { } #endif
This test-only code can be made more useful by accessing the current ``kunit_test``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. Thisis helpful, for example, when providing a fake implementation of a function, orto fail any current test from within an error handler.We can do this via the ``kunit_test`` field in ``task_struct``, which we canaccess 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. IfKUnit is not enabled, or if no test is running in the current task, it willreturn ``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 uses this to implement a "mock" implementation of a function, ``foo``:
.. code-block:: c
#include <kunit/test-bug.h> /* for kunit_get_current_test */
struct test_data { int foo_result; int want_foo_called_with; };
static int fake_foo(int arg) { 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); return test_data->foo_result; }
static void example_simple_test(struct kunit *test) { /* Assume priv (private, a member used to pass test data from * the init function) is allocated in the suite's .init */ struct test_data *test_data = test->priv;
test_data->foo_result = 42; test_data->want_foo_called_with = 1;
/* In a real test, we'd probably pass a pointer to fake_foo somewhere * like an ops struct, etc. instead of calling it directly. */ KUNIT_EXPECT_EQ(test, fake_foo(1), 42); }
In this example, we are using the ``priv`` member of ``struct kunit`` as a wayof passing data to the test from the init function. In general ``priv`` ispointer that can be used for any user data. This is preferred over staticvariables, as it avoids concurrency issues.
Had we wanted something more flexible, we could have used a named ``kunit_resource``.Each test can have multiple resources which have string names providing the sameflexibility as a ``priv`` member, but also, for example, allowing helperfunctions to create resources without conflicting with each other. It is alsopossible to define a clean up function for each resource, making it easy toavoid resource leaks. For more information, see Documentation/dev-tools/kunit/api/resource.rst.
Failing The Current Test------------------------
If we want to fail the current test, we can use ``kunit_fail_current_test(fmt, args...)``which is defined in ``<kunit/test-bug.h>`` and does not require pulling in ``<kunit/test.h>``.For example, we have an option to enable some extra debug checks on some datastructures as shown below:
.. code-block:: c
#include <kunit/test-bug.h>
#ifdef CONFIG_EXTRA_DEBUG_CHECKS static void validate_my_data(struct data *data) { if (is_valid(data)) return;
kunit_fail_current_test("data %p is invalid", data);
/* Normal, non-KUnit, error reporting code here. */ } #else static void my_debug_function(void) { } #endif
``kunit_fail_current_test()`` is safe to call even if KUnit is not enabled. IfKUnit is not enabled, or if no test is running in the current task, it will donothing. This compiles down to either a no-op or a static key check, so willhave 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 willrequire a ``struct device`` or ``struct device_driver``. In many cases, settingup a real device is not required to test any given function, so a fake devicecan be used instead.
KUnit provides helper functions to create and manage these fake devices, whichare internally of type ``struct kunit_device``, and are attached to a special``kunit_bus``. These devices support managed device resources (devres), asdescribed 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 driverwill automatically be destroyed when the corresponding test finishes, but can alsobe manually destroyed with ``driver_unregister()``.
To create a fake device, use the ``kunit_device_register()``, which will createand 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 automaticallycleaned 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()``, andinstead of ``platform_device_register()`` in cases where the device is not otherwisea 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. }