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.. SPDX-License-Identifier: GPL-2.0
============================
Tips For Writing KUnit Tests
============================
Exiting early on failed expectations
------------------------------------
``KUNIT_EXPECT_EQ`` and friends will mark the test as failed and continue
execution. In some cases, it's unsafe to continue and you can use the
``KUNIT_ASSERT`` variant to exit on failure.
.. code-block:: c
void example_test_user_alloc_function(struct kunit *test)
{
void *object = alloc_some_object_for_me();
/* Make sure we got a valid pointer back. */
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, object);
do_something_with_object(object);
}
Allocating memory
-----------------
Where you would use ``kzalloc``, you should prefer ``kunit_kzalloc`` instead.
KUnit will ensure the memory is freed once the test completes.
This is particularly useful since it lets you use the ``KUNIT_ASSERT_EQ``
macros to exit early from a test without having to worry about remembering to
call ``kfree``.
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, "");
}
Testing static functions
------------------------
If you don't want to expose functions or variables just for testing, one option
is to conditionally ``#include`` the test file at the end of your .c file, e.g.
.. 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
------------------------
Similarly to the above, it can be useful to add test-specific logic.
.. 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
TODO(dlatypov@google.com): add an example of using ``current->kunit_test`` in
such a hook when it's not only updated for ``CONFIG_KASAN=y``.
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");
Next Steps
==========
* Optional: see the :doc:`usage` page for a more
in-depth explanation of KUnit.
|
