3 files changed, 122 insertions, 2 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 454f307813ea..0e65cabe08eb 100644
--- a/Documentation/dev-tools/kunit/start.rst
+++ b/Documentation/dev-tools/kunit/start.rst
@@ -196,8 +196,9 @@ Now add the following to ``drivers/misc/Kconfig``:
 .. code-block:: kconfig
 
 	config MISC_EXAMPLE_TEST
-		bool "Test for my example"
+		tristate "Test for my example" if !KUNIT_ALL_TESTS
 		depends on MISC_EXAMPLE && KUNIT=y
+		default KUNIT_ALL_TESTS
 
 and the following to ``drivers/misc/Makefile``:
 
@@ -233,5 +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.