Date:   Wed, 9 Sep 2020 15:51:18 +0000
From:   "Bird, Tim" <Tim.Bird@...y.com>
To:     David Gow <davidgow@...gle.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Alan Maguire <alan.maguire@...cle.com>,
        Randy Dunlap <rd.dunlab@...il.com>,
        Theodore Ts'o <tytso@....edu>, Marco Elver <elver@...gle.com>
CC:     "kunit-dev@...glegroups.com" <kunit-dev@...glegroups.com>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] Documentation: kunit: Add naming guidelines

> -----Original Message-----
> From: David Gow
> 
> 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@...gle.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Reviewed-by: Brendan Higgins <brendanhiggins@...gle.com>
> ---
> 
> This is v2 of the KUnit test nomenclature guidelines. The guidelines have
> changed a bit in response to the discussion on the v1 thread which came
> about after plumbers. The major change is that the filename suffix is
> now "_test", with "_kunit" permitted where it conflicts. There are also
> some other exceptions carved out around existing tests, and very
> non-unit-like tests.
> 
> Changelog:
> 
> v2:
> - Rewrote the filename section to use "_test" as a suffix, and focus on
>   module names, not filenames.
> - Add a motivating introduction, which also calls out existing tests and
>   tests which cause problems when run automatically (long running,
>   flaky tests) as reasons to avoid the guidelines.
> - Talk about including the type of test in the suite name, but only if
>   theres an actual confict. (And update the example for this).
> 
> v1:
> https://lore.kernel.org/linux-kselftest/20200702071416.1780522-1-davidgow@google.com/
> - Fixed a bit of space/tab confusion in the index (Thanks, Randy)
> - Added some more examples (and some test case examples).
> - Added some examples of what not to call subsystems and suites.
> - No longer explicitly require "If unsure, put N" in Kconfig entries.
> - Minor formatting changes
> 
> RFC:
> https://lore.kernel.org/linux-kselftest/20200620054944.167330-1-davidgow@google.com/T/#u
> - Initial version
> 
> 
> The result is a little bit weaker than the previous versions, but
> hopefully will let us get the areas we agree on down.
> 
> -- David
> 
> 
>  Documentation/dev-tools/kunit/index.rst |   1 +
>  Documentation/dev-tools/kunit/style.rst | 207 ++++++++++++++++++++++++
>  2 files changed, 208 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..c234a3ab3c34 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..c001ea1cd87d
> --- /dev/null
> +++ b/Documentation/dev-tools/kunit/style.rst
> @@ -0,0 +1,207 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +===========================
> +Test Style and Nomenclature
> +===========================
> +
> +To make finding, writing, and using KUnit tests as simple as possible, it's
> +strongly encouraged that they are named and written according to the guidelines
> +below. While it's possible to write KUnit tests which do not follow these rules,
> +they may break some tooling, may conflict with other tests, and may not be run
> +automatically by testing systems.
> +
> +It's recommended that you only deviate from these guidelines when:
> +
> +1. Porting tests to KUnit which are already known with an existing name, or
> +2. Writing tests which would cause serious problems if automatically run (e.g.,
> +   nonderministically producing false positives or negatives, or taking an
> +   extremely long time to run).
> +
> +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
> +unless you are actually testing other tests or the kunit framework itself.
> +
> +Example subsystems could be:
> +
> +``ext4``
> +  Matches the module and filesystem name.
> +``apparmor``
> +  Matches the module name and LSM name.
> +``kasan``
> +  Common name for the tool, prominent part of the path ``mm/kasan``
> +``snd_hda_codec_hdmi``
> +  Has several components (``snd``, ``hda``, ``codec``, ``hdmi``) separated by
> +  underscores. Matches the module name.
> +
> +Avoid names like these:
> +
> +``linear-ranges``
> +  Names should use underscores, not dashes, to separate words. Prefer
> +  ``linear_ranges``.
> +``qos-kunit-test``
> +  As well as using underscores, this name should not have "kunit-test" as a
> +  suffix, and ``qos`` is ambiguous as a subsystem name. ``power_qos`` would be a
> +  better name.
> +``pc_parallel_port``
> +  The corresponding module name is ``parport_pc``, so this subsystem should also
> +  be named ``parport_pc``.
> +
> +.. 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.
> +
> +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.
> +
> +In the event that there are multiple types of test using KUnit within a
> +subsystem (e.g., both unit tests and integration tests), they should be put into
> +separate suites, with the type of test as the last element in the suite name.
> +Unless these tests are actually present, avoid using ``_test``, ``_unittest`` or
> +similar in the suite name.
> +
> +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``
> +  Part of the ``ext4`` subsystem, testing the ``inode`` area.
> +``kunit_try_catch``
> +  Part of the ``kunit`` implementation itself, testing the ``try_catch`` area.
> +``apparmor_property_entry``
> +  Part of the ``apparmor`` subsystem, testing the ``property_entry`` area.
> +``kasan``
> +  The ``kasan`` subsystem has only one suite, so the suite name is the same as
> +  the subsystem name.
> +
> +Avoid names like:
> +
> +``ext4_ext4_inode``
> +  There's no reason to state the subsystem twice.
> +``property_entry``
> +  The suite name is ambiguous without the subsystem name.
> +``kasan_integration_test``
> +  Because there is only one suite in the ``kasan`` subsystem, the suite should
> +  just be called ``kasan``. There's no need to redundantly add
> +  ``integration_test``. Should a separate test suite with, for example, unit
> +  tests be added, then that suite could be named ``kasan_unittest`` or similar.
> +
> +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.
> +
> +.. 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.
> +
> +Example test names include:
> +
> +``unpack_u32_with_null_name``
> +  Tests the ``unpack_u32`` function when a NULL name is passed in.
> +``test_list_splice``
> +  Tests the ``list_splice`` macro. It has the prefix ``test_`` to avoid a
> +  name conflict with the macro itself.
> +
> +
> +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
> +
> +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 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 suffic ``_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.
> +
> +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.
> +
> +
> --
> 2.28.0.526.ge36021eeef-goog

Looks good!  I know this was a lot of hard work to get consensus here.
This will help a lot for test frameworks to have consistent and persistent,
fully-qualified names for testcases.  Good job!

Reviewed-by: Tim Bird <tim.bird@...y.com>

 -- Tim

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