Re: [PATCH] Documentation: kunit: Add naming guidelines

[Brendan Higgins <brendanhiggins@google.com>]

I imagine +Theodore Ts'o might have some thoughts on this.

+Bird, Timothy - Figured you might be interested since I think this
might pertain to the KTAP discussion.

On Fri, Jun 19, 2020 at 10:50 PM David Gow <davidgow@google.com> wrote:
>
> As discussed in [1], KUnit tests have hitherto not had a particularly
> consistent naming scheme. This adds documentation outlining how tests
> and test suites should be named, including how those names should be
> used in Kconfig entries and filenames.
>
> [1]:
> https://lore.kernel.org/linux-kselftest/202006141005.BA19A9D3@keescook/t/#u
>
> Signed-off-by: David Gow <davidgow@google.com>
> ---
> This is a first draft of some naming guidelines for KUnit tests. Note
> that I haven't edited it for spelling/grammar/style yet: I wanted to get
> some feedback on the actual naming conventions first.
>
> The issues which came most to the forefront while writing it were:
> - Do we want to make subsystems a more explicit thing (make the KUnit
>   framework recognise them, make suites KTAP subtests of them, etc)
>   - I'm leaning towards no, mainly because it doesn't seem necessary,
>     and it makes the subsystem-with-only-one-suite case ugly.
>
> - Do we want to support (or encourage) Kconfig options and/or modules at
>   the subsystem level rather than the suite level?
>   - This could be nice: it'd avoid the proliferation of a large number
>     of tiny config options and modules, and would encourage the test for
>     <module> to be <module>_kunit, without other stuff in-between.
>
> - As test names are also function names, it may actually make sense to
>   decorate them with "test" or "kunit" or the like.
>   - If we're testing a function "foo", "test_foo" seems like as good a
>     name for the function as any. Sure, many cases may could have better
>     names like "foo_invalid_context" or something, but that won't make
>     sense for everything.
>   - Alternatively, do we split up the test name and the name of the
>     function implementing the test?
>
> Thoughts?

Overall it looks pretty good. I would like to see some examples
fleshed out a bit more or at least say how things like subsystem names
are used, but otherwise this looks good to me.

>  Documentation/dev-tools/kunit/index.rst |   1 +
>  Documentation/dev-tools/kunit/style.rst | 139 ++++++++++++++++++++++++
>  2 files changed, 140 insertions(+)
>  create mode 100644 Documentation/dev-tools/kunit/style.rst
>
> diff --git a/Documentation/dev-tools/kunit/index.rst b/Documentation/dev-tools/kunit/index.rst
> index e93606ecfb01..117c88856fb3 100644
> --- a/Documentation/dev-tools/kunit/index.rst
> +++ b/Documentation/dev-tools/kunit/index.rst
> @@ -11,6 +11,7 @@ KUnit - Unit Testing for the Linux Kernel
>         usage
>         kunit-tool
>         api/index
> +        style
>         faq
>
>  What is KUnit?
> diff --git a/Documentation/dev-tools/kunit/style.rst b/Documentation/dev-tools/kunit/style.rst
> new file mode 100644
> index 000000000000..9363b5607262
> --- /dev/null
> +++ b/Documentation/dev-tools/kunit/style.rst
> @@ -0,0 +1,139 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +===========================
> +Test Style and Nomenclature
> +===========================
> +
> +Subsystems, Suites, and Tests
> +=============================
> +
> +In order to make tests as easy to find as possible, they're grouped into suites
> +and subsystems. A test suite is a group of tests which test a related area of
> +the kernel, and a subsystem is a set of test suites which test different parts
> +of the same kernel subsystem or driver.
> +
> +Subsystems
> +----------
> +
> +Every test suite must belong to a subsystem. A subsystem is a collection of one
> +or more KUnit test suites which test the same driver or part of the kernel. A
> +rule of thumb is that a test subsystem should match a single kernel module. If
> +the code being tested can't be compiled as a module, in many cases the subsystem
> +should correspond to a directory in the source tree or an entry in the
> +MAINTAINERS file. If unsure, follow the conventions set by tests in similar
> +areas.
> +
> +Test subsystems should be named after the code being tested, either after the
> +module (wherever possible), or after the directory or files being tested. Test
> +subsystems should be named to avoid ambiguity where necessary.
> +
> +If a test subsystem name has multiple components, they should be separated by
> +underscores. Do not include "test" or "kunit" directly in the subsystem name

nit: Embolden "Do not".

> +unless you are actually testing other tests or the kunit framework itself.
> +
> +Example subsystems could be:
> +
> +* ``ext4``
> +* ``apparmor``
> +* ``kasan``

Maybe add some examples that exercise the "multiple components ...
separated by underscores". Some negative examples might also be good
since we currently violate this rule.

> +.. note::
> +        The KUnit API and tools do not explicitly know about subsystems. They're
> +        simply a way of categorising test suites and naming modules which
> +        provides a simple, consistent way for humans to find and run tests. This
> +        may change in the future, though.

I think we should have some way to enshrine this in KUnit, if not via
code, I think we should at least say how the convention is used.

> +Suites
> +------
> +
> +KUnit tests are grouped into test suites, which cover a specific area of
> +functionality being tested. Test suites can have shared initialisation and
> +shutdown code which is run for all tests in the suite.
> +Not all subsystems will need to be split into multiple test suites (e.g. simple drivers).
> +
> +Test suites are named after the subsystem they are part of. If a subsystem
> +contains several suites, the specific area under test should be appended to the
> +subsystem name, separated by an underscore.
> +
> +The full test suite name (including the subsystem name) should be specified as
> +the ``.name`` member of the ``kunit_suite`` struct, and forms the base for the
> +module name (see below).
> +
> +Example test suites could include:
> +
> +* ``ext4_inode``
> +* ``kunit_try_catch``
> +* ``apparmor_property_entry``
> +* ``kasan``
> +
> +Tests

nit: "Test Cases".

> +-----
> +
> +Individual tests consist of a single function which tests a constrained
> +codepath, property, or function. In the test output, individual tests' results
> +will show up as subtests of the suite's results.
> +
> +Tests should be named after what they're testing. This is often the name of the
> +function being tested, with a description of the input or codepath being tested.
> +As tests are C functions, they should be named and written in accordance with
> +the kernel coding style.

Can you add an example?

> +.. note::
> +        As tests are themselves functions, their names cannot conflict with
> +        other C identifiers in the kernel. This may require some creative
> +        naming. It's a good idea to make your test functions `static` to avoid
> +        polluting the global namespace.
> +
> +Should it be necessary to refer to a test outside the context of its test suite,
> +the *fully-qualified* name of a test should be the suite name followed by the
> +test name, separated by a colon (i.e. ``suite:test``).
> +
> +Test Kconfig Entries
> +====================
> +
> +Every test suite should be tied to a Kconfig entry.
> +
> +This Kconfig entry must:
> +
> +* be named ``CONFIG_<name>_KUNIT_TEST``: where <name> is the name of the test
> +  suite.
> +* be listed either alongside the config entries for the driver/subsystem being
> +  tested, or be under [Kernel Hacking]→[Kernel Testing and Coverage]
> +* depend on ``CONFIG_KUNIT``
> +* be visible only if ``CONFIG_KUNIT_ALL_TESTS`` is not enabled.
> +* have a default value of ``CONFIG_KUNIT_ALL_TESTS``.
> +* have a brief description of KUnit in the help text
> +* include "If unsure, say N" in the help text
> +
> +Unless there's a specific reason not to (e.g. the test is unable to be built as
> +a module), Kconfig entries for tests should be tristate.
> +
> +An example Kconfig entry:
> +
> +.. code-block:: none
> +
> +        config FOO_KUNIT_TEST
> +                tristate "KUnit test for foo" if !KUNIT_ALL_TESTS
> +                depends on KUNIT
> +                default KUNIT_ALL_TESTS
> +                help
> +                    This builds unit tests for foo.
> +
> +                    For more information on KUnit and unit tests in general, please refer
> +                    to the KUnit documentation in Documentation/dev-tools/kunit
> +
> +                    If unsure, say N
> +
> +
> +Test Filenames
> +==============
> +
> +Where possible, test suites should be placed in a separate source file in the
> +same directory as the code being tested.
> +
> +This file should be named ``<suite>_kunit.c``. It may make sense to strip
> +excessive namespacing from the source filename (e.g., ``firmware_kunit.c`` instead of
> +``<drivername>_firmware.c``), but please ensure the module name does contain the
> +full suite name.
> +
> +
> --
> 2.27.0.111.gc72c7da667-goog
>