linux-kernel - Re: [PATCH v4 4/4] kunit: tool: support running each suite/test separately

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Date:   Wed, 6 Oct 2021 10:22:07 -0700
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     Daniel Latypov <dlatypov@...gle.com>
Cc:     davidgow@...gle.com, linux-kernel@...r.kernel.org,
        kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org,
        skhan@...uxfoundation.org
Subject: Re: [PATCH v4 4/4] kunit: tool: support running each suite/test separately

On Thu, Sep 30, 2021 at 3:21 PM Daniel Latypov <dlatypov@...gle.com> wrote:
>
> The new --run_isolated flag makes the tool boot the kernel once per
> suite or test, preventing leftover state from one suite to impact the
> other. This can be useful as a starting point to debugging test
> hermeticity issues.
>
> Note: it takes a lot longer, so people should not use it normally.
>
> Consider the following very simplified example:
>
>   bool disable_something_for_test = false;
>   void function_being_tested() {
>     ...
>     if (disable_something_for_test) return;
>     ...
>   }
>
>   static void test_before(struct kunit *test)
>   {
>     disable_something_for_test = true;
>     function_being_tested();
>     /* oops, we forgot to reset it back to false */
>   }
>
>   static void test_after(struct kunit *test)
>   {
>     /* oops, now "fixing" test_before can cause test_after to fail! */
>     function_being_tested();
>   }
>
> Presented like this, the issues are obvious, but it gets a lot more
> complicated to track down as the amount of test setup and helper
> functions increases.
>
> Another use case is memory corruption. It might not be surfaced as a
> failure/crash in the test case or suite that caused it. I've noticed in
> kunit's own unit tests, the 3rd suite after might be the one to finally
> crash after an out-of-bounds write, for example.
>
> Example usage:
>
> Per suite:
> $ ./tools/testing/kunit/kunit.py run --kunitconfig=lib/kunit --run_isolated=suite
> ...
> Starting KUnit Kernel (1/7)...
> ============================================================
> ======== [PASSED] kunit_executor_test ========
> ....
> Testing complete. 5 tests run. 0 failed. 0 crashed. 0 skipped.
> Starting KUnit Kernel (2/7)...
> ============================================================
> ======== [PASSED] kunit-try-catch-test ========
> ...
>
> Per test:
> $ ./tools/testing/kunit/kunit.py run --kunitconfig=lib/kunit --run_isolated=test
> Starting KUnit Kernel (1/23)...
> ============================================================
> ======== [PASSED] kunit_executor_test ========
> [PASSED] parse_filter_test
> ============================================================
> Testing complete. 1 tests run. 0 failed. 0 crashed. 0 skipped.
> Starting KUnit Kernel (2/23)...
> ============================================================
> ======== [PASSED] kunit_executor_test ========
> [PASSED] filter_subsuite_test
> ...
>
> It works with filters as well:
> $ ./tools/testing/kunit/kunit.py run --kunitconfig=lib/kunit --run_isolated=suite example
> ...
> Starting KUnit Kernel (1/1)...
> ============================================================
> ======== [PASSED] example ========
> ...
>
> It also handles test filters, '*.*skip*' runs these 3 tests:
>   kunit_status.kunit_status_mark_skipped_test
>   example.example_skip_test
>   example.example_mark_skipped_test
>
> Signed-off-by: Daniel Latypov <dlatypov@...gle.com>
> Reviewed-by: David Gow <davidgow@...gle.com>

Reviewed-by: Brendan Higgins <brendanhiggins@...gle.com>