Re: [PATCH v2] Documentation: KUnit: Update filename best practices

[David Gow]

On Sun, 21 Jul 2024 at 00:54, Kees Cook <kees@xxxxxxxxxx> wrote:
>
> Based on feedback from Linus[1] and follow-up discussions, change the
> suggested file naming for KUnit tests.
>
> Link: https://lore.kernel.org/lkml/CAHk-=wgim6pNiGTBMhP8Kd3tsB7_JTAuvNJ=XYd3wPvvk=OHog@xxxxxxxxxxxxxx/ [1]
> Signed-off-by: Kees Cook <kees@xxxxxxxxxx>
> ---
> Cc: David Gow <davidgow@xxxxxxxxxx>
> Cc: Brendan Higgins <brendan.higgins@xxxxxxxxx>
> Cc: Rae Moar <rmoar@xxxxxxxxxx>
> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: linux-kselftest@xxxxxxxxxxxxxxx
> Cc: kunit-dev@xxxxxxxxxxxxxxxx
> Cc: linux-doc@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-hardening@xxxxxxxxxxxxxxx
> ---

Thanks again for dealing with this, Kees.

>  Documentation/dev-tools/kunit/style.rst | 25 +++++++++++++++----------
>  1 file changed, 15 insertions(+), 10 deletions(-)
>
> diff --git a/Documentation/dev-tools/kunit/style.rst b/Documentation/dev-tools/kunit/style.rst
> index b6d0d7359f00..1538835cd0e2 100644
> --- a/Documentation/dev-tools/kunit/style.rst
> +++ b/Documentation/dev-tools/kunit/style.rst
> @@ -188,15 +188,20 @@ For example, a Kconfig entry might look like:
>  Test File and Module Names
>  ==========================
>
> -KUnit tests can often be compiled as a module. These modules should be named
> -after the test suite, followed by ``_test``. If this is likely to conflict with
> -non-KUnit tests, the suffix ``_kunit`` can also be used.
> -
> -The easiest way of achieving this is to name the file containing the test suite
> -``<suite>_test.c`` (or, as above, ``<suite>_kunit.c``). This file should be
> -placed next to the code under test.
> +Whether a KUnit test is compiled as a separate module or via an
> +``#include`` in a core kernel source file, the file should be named
> +after the test suite, followed by ``_kunit``, and live in a ``tests``
> +subdirectory to avoid conflicting with regular modules (e.g. if "foobar"
> +is the core module, then "foobar_kunit" is the KUnit test module) or the
> +core kernel source file names (e.g. for tab-completion). Many existing
> +tests use a ``_test`` suffix, but this is considered deprecated.

I think John's updated version here is better. Personally, I'd rather
the bit about module names lead here, as I think that's the part most
likely to cause actual issues, and the source file name bit is more of
a "here are problems to avoid, and sensible defaults which avoid them"
than "here's an utterly inviolable rule".

Maybe:
```
KUnit tests are often compiled as a separate module. To avoid
conflicting with regular modules, KUnit modules should be named after
the test suite, followed by ``_kunit`` (e.g. if
"foobar" is the core module, then "foobar_kunit" is the KUnit test module).

Test source files, whether compiled as a separate module or an
``#include`` in another source file, are best kept in a ``tests/
subdirectory to not conflict with other source files (e.g. for
tab-completion).

Note that the ``_test`` suffix has also been used in some existing
tests. The ``_kunit`` suffix is preferred, as it makes the distinction
between KUnit and non-KUnit tests clearer.
```

(But this is all largely bikeshedding at this point. As long as we end
up describing the sensible defaults, and don't paint ourselves (and
subsystem maintainers) into a corner, either should work.

> +
> +So for the common case, name the file containing the test suite
> +``tests/<suite>_kunit.c``. The ``tests`` directory should be placed at
> +the same level as the code under test. For example, tests for
> +``lib/string.c`` live in ``lib/tests/string_kunit.c``.
>
>  If the suite name contains some or all of the name of the test's parent
> -directory, it may make sense to modify the source filename to reduce redundancy.
> -For example, a ``foo_firmware`` suite could be in the ``foo/firmware_test.c``
> -file.
> +directory, it may make sense to modify the source filename to reduce
> +redundancy. For example, a ``foo_firmware`` suite could be in the
> +``tests/foo/firmware_kunit.c`` file.

I think that this should be ``foo/tests/firmware_kunit.c``. I'd even
be okay with ``foo/tests/firmware.c``, as the module name needs
manually updating in the makefile anyway, where it should either be
``foo_firmware_kunit``, or included in a larger ``foo_kunit`` module.

-- David

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