Documentation: kunit: Warn that exit functions run even if init fails

KUnit's exit functions will run even if the corresponding init function
fails. It's easy, when writing an exit function, to assume the init
function succeeded, and (for example) access uninitialised memory or
dereference NULL pointers.

Note that this case exists and should be handled in the documentation.

Suggested-by: Benjamin Berg <benjamin@sipsolutions.net>
Link: https://lore.kernel.org/linux-kselftest/a39af0400abedb2e9b31d84c37551cecc3eed0e1.camel@sipsolutions.net/
Reviewed-by: Sadiya Kazi <sadiyakazi@google.com>
Signed-off-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Documentation/dev-tools/kunit/usage.rst

@@ -166,7 +166,12 @@ many similar tests. In order to reduce duplication in these closely related
 tests, 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 code
 with optional setup and teardown functions that run before/after the whole
-suite and/or every test case. For example:
+suite 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
 
@@ -196,7 +201,10 @@ after everything else. ``kunit_test_suite(example_test_suite)`` registers the
 test suite with the KUnit test framework.
 
 .. note::
-   A test case will only run if it is associated with a test suite.
+   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 the
 specified test suite in a special linker section so that it can be run by KUnit

include/kunit/test.h

@@ -168,6 +168,9 @@ static inline char *kunit_status_to_ok_not_ok(enum kunit_status status)
  * test case, similar to the notion of a *test fixture* or a *test class*
  * in other unit testing frameworks like JUnit or Googletest.
  *
+ * Note that @exit and @suite_exit will run even if @init or @suite_init
+ * fail: make sure they can handle any inconsistent state which may result.
+ *
  * Every &struct kunit_case must be associated with a kunit_suite for KUnit
  * to run it.
  */