RE: [PATCH] Documentation: kunit: Make the KUnit documentation less UML-specific

Bird, Tim
2020-02-11T18:26:34Z

> -----Original Message-----
> From: David Gow
> Sent: Monday, February 10, 2020 6:02 PM
>
> Remove some of the outmoded "Why KUnit" rationale -- which focuses
> significantly on UML -- and update the Getting Started guide to mention
> running tests without the kunit_tool wrapper.

Yeah... I don't like the removal of some of the rationale. There were
significant discussions about kunit prior to its acceptance into mainline, and
many people are still unfamiliar with the system (and with automated testing
in general). I think it's worth keeping some of the rationale, to avoid rehashing
these discussions. Especially the part about speed changing the nature of test
usage should be, IMHO, kept.

I think reworking anything that has to do with UML is OK.

Detailed feedback below.

> Signed-off-by: David Gow <davidgow@google.com>
> ---
> This is an attempt at resolving some of the issues with the KUnit
> documentation pointed out here:
> https://lore.kernel.org/linux-kselftest/CABVgOSkiLi0UNijH1xTSvmsJEE5+ocCZ7nkzmKzxDLzzfqBSzQ@mail.gmail.com/
>
> There's definitely room for further work on the KUnit documentation
> (e.g., adding more information around the environment tests run in), but
> this hopefully is better than nothing as a starting point.
>
>
> Documentation/dev-tools/kunit/index.rst | 60 ++++---------------
> Documentation/dev-tools/kunit/start.rst | 80 +++++++++++++++++++++----
> 2 files changed, 78 insertions(+), 62 deletions(-)
>
> diff --git a/Documentation/dev-tools/kunit/index.rst b/Documentation/dev-tools/kunit/index.rst
> index d16a4d2c3a41..6064cd14dfad 100644
> --- a/Documentation/dev-tools/kunit/index.rst
> +++ b/Documentation/dev-tools/kunit/index.rst
> @@ -17,63 +17,23 @@ What is KUnit?
> ==============
>
> KUnit is a lightweight unit testing and mocking framework for the Linux kernel.
> -These tests are able to be run locally on a developer's workstation without a VM
> -or special hardware.
How about just changing that to:
Many of these tests can be run locally on a developer's workstation without a VM
or special hardware.
>
> KUnit is heavily inspired by JUnit, Python's unittest.mock, and
> Googletest/Googlemock for C++. KUnit provides facilities for defining unit test
> cases, grouping related test cases into test suites, providing common
> infrastructure for running tests, and much more.
>
> -Get started now: :doc:`start`
> -
> -Why KUnit?
> -==========
> -
> -A unit test is supposed to test a single unit of code in isolation, hence the
> -name. A unit test should be the finest granularity of testing and as such should
> -allow all possible code paths to be tested in the code under test; this is only
> -possible if the code under test is very small and does not have any external
> -dependencies outside of the test's control like hardware.
I'm not sure why this paragraph was removed. It stands to contrast kunit
from other kselftest or higher-level test suites.
> -
> -Outside of KUnit, there are no testing frameworks currently
> -available for the kernel that do not require installing the kernel on a test
> -machine or in a VM and all require tests to be written in userspace running on
> -the kernel; this is true for Autotest, and kselftest, disqualifying
> -any of them from being considered unit testing frameworks.

This paragraph seems like it might become dated, and is pretty specific to
the UML architecture, so I agree with removing it.

> +KUnit consists of a kernel component, which provides a set of macros for easily
> +writing unit tests. Tests written against KUnit will run on kernel boot if
> +built-in, or when loaded if built as a module. These tests write out results to
> +the kernel log in `TAP <https://testanything.org/>`_ format.
>
> -KUnit addresses the problem of being able to run tests without needing a virtual
> -machine or actual hardware with User Mode Linux. User Mode Linux is a Linux
> -architecture, like ARM or x86; however, unlike other architectures it compiles
> -to a standalone program that can be run like any other program directly inside
> -of a host operating system; to be clear, it does not require any virtualization
> -support; it is just a regular program.
> +To make running these tests (and reading the results) easier, KUnit offsers
> +:doc:`kunit_tool <kunit-tool>`, which builds a `User Mode Linux
> +<http://user-mode-linux.sourceforge.net>`_ kernel, runs it, and parses the test
> +results. This provides a quick way of running KUnit tests during development.

IMHO you've dropped some valuable information about how the UML case works.
Is it still supported? In that case, explaining how it works is useful, even if it's not
the only method to invoke the tests.

> -Alternatively, kunit and kunit tests can be built as modules and tests will
> -run when the test module is loaded.
> -
> -KUnit is fast. Excluding build time, from invocation to completion KUnit can run
> -several dozen tests in only 10 to 20 seconds; this might not sound like a big
> -deal to some people, but having such fast and easy to run tests fundamentally
> -changes the way you go about testing and even writing code in the first place.
> -Linus himself said in his `git talk at Google
> -<https://gist.github.com/lorn/1272686/revisions#diff-53c65572127855f1b003db4064a94573R874>`_:
> -
> - "... a lot of people seem to think that performance is about doing the
> - same thing, just doing it faster, and that is not true. That is not what
> - performance is all about. If you can do something really fast, really
> - well, people will start using it differently."
> -
> -In this context Linus was talking about branching and merging,
> -but this point also applies to testing. If your tests are slow, unreliable, are
> -difficult to write, and require a special setup or special hardware to run,
> -then you wait a lot longer to write tests, and you wait a lot longer to run
> -tests; this means that tests are likely to break, unlikely to test a lot of
> -things, and are unlikely to be rerun once they pass. If your tests are really
> -fast, you run them all the time, every time you make a change, and every time
> -someone sends you some code. Why trust that someone ran all their tests
> -correctly on every change when you can just run them yourself in less time than
> -it takes to read their test log?
> +Get started now: :doc:`start`

I think this whole section should be kept. It's true that the tests should be fast
whether you're using UML or not. Whether the non-UML version of testing is
fast *enough* is a matter of opinion. The above is a good guiding principle for unit
tests whether they are executed using UML or not.

The rest of the changes look good (at least, I'm not qualified to judge them.)
-- Tim

>
> How do I use it?
> ================
> @@ -81,3 +41,5 @@ How do I use it?
> * :doc:`start` - for new users of KUnit
> * :doc:`usage` - for a more detailed explanation of KUnit features
> * :doc:`api/index` - for the list of KUnit APIs used for testing
> +* :doc:`kunit-tool` - for more information on the kunit_tool helper script
> +* :doc:`faq` - for answers to some common questions about KUnit
> diff --git a/Documentation/dev-tools/kunit/start.rst b/Documentation/dev-tools/kunit/start.rst
> index 4e1d24db6b13..e1c5ce80ce12 100644
> --- a/Documentation/dev-tools/kunit/start.rst
> +++ b/Documentation/dev-tools/kunit/start.rst
> @@ -9,11 +9,10 @@ Installing dependencies
> KUnit has the same dependencies as the Linux kernel. As long as you can build
> the kernel, you can run KUnit.
>
> -KUnit Wrapper
> -=============
> -Included with KUnit is a simple Python wrapper that helps format the output to
> -easily use and read KUnit output. It handles building and running the kernel, as
> -well as formatting the output.
> +Running tests with the KUnit Wrapper
> +====================================
> +Included with KUnit is a simple Python wrapper which runs tests under User Mode
> +Linux, and formats the test results.
>
> The wrapper can be run with:
>
> @@ -21,22 +20,42 @@ The wrapper can be run with:
>
> ./tools/testing/kunit/kunit.py run --defconfig
>
> -For more information on this wrapper (also called kunit_tool) checkout the
> +For more information on this wrapper (also called kunit_tool) check out the
> :doc:`kunit-tool` page.
>
> Creating a .kunitconfig
> -=======================
> -The Python script is a thin wrapper around Kbuild. As such, it needs to be
> -configured with a ``.kunitconfig`` file. This file essentially contains the
> -regular Kernel config, with the specific test targets as well.
> -
> +-----------------------
> +If you want to run a specific set of tests (rather than those listed in the
> +KUnit defconfig), you can provide Kconfig options in the ``.kunitconfig`` file.
> +This file essentially contains the regular Kernel config, with the specific
> +test targets as well. The ``.kunitconfig`` should also contain any other config
> +options required by the tests.
> +
> +A good starting point for a ``.kunitconfig`` is the KUnit defconfig:
> .. code-block:: bash
>
> cd $PATH_TO_LINUX_REPO
> cp arch/um/configs/kunit_defconfig .kunitconfig
>
> -Verifying KUnit Works
> ----------------------
> +You can then add any other Kconfig options you wish, e.g.:
> +.. code-block:: none
> +
> + CONFIG_LIST_KUNIT_TEST=y
> +
> +:doc:`kunit_tool <kunit-tool>` will ensure that all config options set in
> +``.kunitconfig`` are set in the kernel ``.config`` before running the tests.
> +It'll warn you if you haven't included the dependencies of the options you're
> +using.
> +
> +.. note::
> + Note that removing something from the ``.kunitconfig`` will not trigger a
> + rebuild of the ``.config`` file: the configuration is only updated if the
> + ``.kunitconfig`` is not a subset of ``.config``. This means that you can use
> + other tools (such as make menuconfig) to adjust other config options.
> +
> +
> +Running the tests
> +-----------------
>
> To make sure that everything is set up correctly, simply invoke the Python
> wrapper from your kernel repo:
> @@ -62,6 +81,41 @@ followed by a list of tests that are run. All of them should be passing.
> Because it is building a lot of sources for the first time, the
> ``Building KUnit kernel`` step may take a while.
>
> +Running tests without the KUnit Wrapper
> +=======================================
> +
> +If you'd rather not use the KUnit Wrapper (if, for example, you need to
> +integrate with other systems, or use an architecture other than UML), KUnit can
> +be included in any kernel, and the results read out and parsed manually.
> +
> +.. note::
> + KUnit is not designed for use in a production system, and it's possible that
> + tests may reduce the stability or security of the system.
> +
> +
> +
> +Configuring the kernel
> +----------------------
> +
> +In order to enable KUnit itself, you simply need to enable the ``CONFIG_KUNIT``
> +Kconfig option (it's under Kernel Hacking/Kernel Testing and Coverage in
> +menuconfig). From there, you can enable any KUnit tests you want: they usually
> +have config options ending in ``_KUNIT_TEST``.
> +
> +KUnit and KUnit tests can be compiled as modules: in this case the tests in a
> +module will be run when the module is loaded.
> +
> +Running the tests
> +-----------------
> +
> +Build and run your kernel as usual. Test output will be written to the kernel
> +log in `TAP <https://testanything.org/>`_ format.
> +
> +.. note::
> + It's possible that there will be other lines and/or data interspersed in the
> + TAP output.
> +
> +
> Writing your first test
> =======================
>
> --
> 2.25.0.341.g760bfbb309-goog