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| -rw-r--r-- | Documentation/dev-tools/kunit/index.rst | 2 | ||||
| -rw-r--r-- | Documentation/dev-tools/kunit/start.rst | 4 | ||||
| -rw-r--r-- | Documentation/dev-tools/kunit/tips.rst | 115 |
3 files changed, 120 insertions, 1 deletions
diff --git a/Documentation/dev-tools/kunit/index.rst b/Documentation/dev-tools/kunit/index.rst index c234a3ab3c34..848478838347 100644 --- a/Documentation/dev-tools/kunit/index.rst +++ b/Documentation/dev-tools/kunit/index.rst @@ -13,6 +13,7 @@ KUnit - Unit Testing for the Linux Kernel api/index style faq + tips What is KUnit? ============== @@ -88,6 +89,7 @@ How do I use it? ================ * :doc:`start` - for new users of KUnit +* :doc:`tips` - for short examples of best practices * :doc:`usage` - for a more detailed explanation of KUnit features * :doc:`api/index` - for the list of KUnit APIs used for testing * :doc:`kunit-tool` - for more information on the kunit_tool helper script diff --git a/Documentation/dev-tools/kunit/start.rst b/Documentation/dev-tools/kunit/start.rst index 560f27af4619..0e65cabe08eb 100644 --- a/Documentation/dev-tools/kunit/start.rst +++ b/Documentation/dev-tools/kunit/start.rst @@ -234,5 +234,7 @@ Congrats! You just wrote your first KUnit test! Next Steps ========== -* Check out the :doc:`usage` page for a more +* Check out the :doc:`tips` page for tips on + writing idiomatic KUnit tests. +* Optional: see the :doc:`usage` page for a more in-depth explanation of KUnit. diff --git a/Documentation/dev-tools/kunit/tips.rst b/Documentation/dev-tools/kunit/tips.rst new file mode 100644 index 000000000000..a6ca0af14098 --- /dev/null +++ b/Documentation/dev-tools/kunit/tips.rst @@ -0,0 +1,115 @@ +.. 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. |