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![Mauro Carvalho Chehab](/assets/img/avatar_default.png)
The :doc:`foo` tag is auto-generated via automarkup.py. So, use the filename at the sources, instead of :doc:`foo`. Reviewed-by: David Gow <davidgow@google.com> Acked-by: Brendan Higgins <brendanhiggins@google.com> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org> Link: https://lore.kernel.org/r/6fde409079959a95b62b9b2692503608d7ff0dbd.1623824363.git.mchehab+huawei@kernel.org Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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190 lines
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.. SPDX-License-Identifier: GPL-2.0
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============================
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Tips For Writing KUnit Tests
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============================
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Exiting early on failed expectations
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------------------------------------
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``KUNIT_EXPECT_EQ`` and friends will mark the test as failed and continue
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execution. In some cases, it's unsafe to continue and you can use the
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``KUNIT_ASSERT`` variant to exit on failure.
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.. code-block:: c
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void example_test_user_alloc_function(struct kunit *test)
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{
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void *object = alloc_some_object_for_me();
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/* Make sure we got a valid pointer back. */
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KUNIT_ASSERT_NOT_ERR_OR_NULL(test, object);
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do_something_with_object(object);
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}
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Allocating memory
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-----------------
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Where you would use ``kzalloc``, you should prefer ``kunit_kzalloc`` instead.
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KUnit will ensure the memory is freed once the test completes.
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This is particularly useful since it lets you use the ``KUNIT_ASSERT_EQ``
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macros to exit early from a test without having to worry about remembering to
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call ``kfree``.
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Example:
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.. code-block:: c
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void example_test_allocation(struct kunit *test)
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{
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char *buffer = kunit_kzalloc(test, 16, GFP_KERNEL);
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/* Ensure allocation succeeded. */
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KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buffer);
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KUNIT_ASSERT_STREQ(test, buffer, "");
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}
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Testing static functions
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------------------------
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If you don't want to expose functions or variables just for testing, one option
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is to conditionally ``#include`` the test file at the end of your .c file, e.g.
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.. code-block:: c
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/* In my_file.c */
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static int do_interesting_thing();
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#ifdef CONFIG_MY_KUNIT_TEST
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#include "my_kunit_test.c"
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#endif
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Injecting test-only code
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------------------------
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Similarly to the above, it can be useful to add test-specific logic.
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.. code-block:: c
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/* In my_file.h */
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#ifdef CONFIG_MY_KUNIT_TEST
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/* Defined in my_kunit_test.c */
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void test_only_hook(void);
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#else
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void test_only_hook(void) { }
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#endif
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This test-only code can be made more useful by accessing the current kunit
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test, see below.
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Accessing the current test
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--------------------------
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In some cases, you need to call test-only code from outside the test file, e.g.
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like in the example above or if you're providing a fake implementation of an
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ops struct.
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There is a ``kunit_test`` field in ``task_struct``, so you can access it via
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``current->kunit_test``.
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Here's a slightly in-depth example of how one could implement "mocking":
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.. code-block:: c
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#include <linux/sched.h> /* for current */
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struct test_data {
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int foo_result;
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int want_foo_called_with;
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};
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static int fake_foo(int arg)
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{
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struct kunit *test = current->kunit_test;
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struct test_data *test_data = test->priv;
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KUNIT_EXPECT_EQ(test, test_data->want_foo_called_with, arg);
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return test_data->foo_result;
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}
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static void example_simple_test(struct kunit *test)
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{
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/* Assume priv is allocated in the suite's .init */
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struct test_data *test_data = test->priv;
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test_data->foo_result = 42;
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test_data->want_foo_called_with = 1;
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/* In a real test, we'd probably pass a pointer to fake_foo somewhere
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* like an ops struct, etc. instead of calling it directly. */
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KUNIT_EXPECT_EQ(test, fake_foo(1), 42);
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}
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Note: here we're able to get away with using ``test->priv``, but if you wanted
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something more flexible you could use a named ``kunit_resource``, see
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Documentation/dev-tools/kunit/api/test.rst.
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Failing the current test
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------------------------
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But sometimes, you might just want to fail the current test. In that case, we
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have ``kunit_fail_current_test(fmt, args...)`` which is defined in ``<kunit/test-bug.h>`` and
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doesn't require pulling in ``<kunit/test.h>``.
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E.g. say we had an option to enable some extra debug checks on some data structure:
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.. code-block:: c
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#include <kunit/test-bug.h>
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#ifdef CONFIG_EXTRA_DEBUG_CHECKS
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static void validate_my_data(struct data *data)
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{
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if (is_valid(data))
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return;
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kunit_fail_current_test("data %p is invalid", data);
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/* Normal, non-KUnit, error reporting code here. */
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}
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#else
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static void my_debug_function(void) { }
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#endif
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Customizing error messages
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--------------------------
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Each of the ``KUNIT_EXPECT`` and ``KUNIT_ASSERT`` macros have a ``_MSG`` variant.
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These take a format string and arguments to provide additional context to the automatically generated error messages.
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.. code-block:: c
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char some_str[41];
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generate_sha1_hex_string(some_str);
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/* Before. Not easy to tell why the test failed. */
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KUNIT_EXPECT_EQ(test, strlen(some_str), 40);
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/* After. Now we see the offending string. */
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KUNIT_EXPECT_EQ_MSG(test, strlen(some_str), 40, "some_str='%s'", some_str);
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Alternatively, one can take full control over the error message by using ``KUNIT_FAIL()``, e.g.
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.. code-block:: c
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/* Before */
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KUNIT_EXPECT_EQ(test, some_setup_function(), 0);
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/* After: full control over the failure message. */
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if (some_setup_function())
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KUNIT_FAIL(test, "Failed to setup thing for testing");
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Next Steps
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==========
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* Optional: see the Documentation/dev-tools/kunit/usage.rst page for a more
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in-depth explanation of KUnit.
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