Message-ID: <BYAPR13MB250396DFE4C15CF64C0834A7FD6E9@BYAPR13MB2503.namprd13.prod.outlook.com>
Date:   Tue, 7 Dec 2021 17:11:13 +0000
From:   <Tim.Bird@...y.com>
To:     <sharinder@...gle.com>, <davidgow@...gle.com>,
        <brendanhiggins@...gle.com>, <shuah@...nel.org>, <corbet@....net>
CC:     <linux-kselftest@...r.kernel.org>, <kunit-dev@...glegroups.com>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 1/7] Documentation: KUnit: Rewrite main page

See one additional suggestion below.
 -- Tim


> -----Original Message-----
> From: Harinder Singh <sharinder@...gle.com>
> 
> Add a section on advantages of unit testing, how to write unit tests,
> KUnit features and Prerequisites.
> 
> Signed-off-by: Harinder Singh <sharinder@...gle.com>
> ---
>  Documentation/dev-tools/kunit/index.rst | 166 +++++++++++++-----------
>  1 file changed, 88 insertions(+), 78 deletions(-)
> 
> diff --git a/Documentation/dev-tools/kunit/index.rst b/Documentation/dev-tools/kunit/index.rst
> index cacb35ec658d..ebf4bffaa1ca 100644
> --- a/Documentation/dev-tools/kunit/index.rst
> +++ b/Documentation/dev-tools/kunit/index.rst
> @@ -1,11 +1,12 @@
>  .. SPDX-License-Identifier: GPL-2.0
> 
> -=========================================
> -KUnit - Unit Testing for the Linux Kernel
> -=========================================
> +=================================
> +KUnit - Linux Kernel Unit Testing
> +=================================
> 
>  .. toctree::
>  	:maxdepth: 2
> +	:caption: Contents:
> 
>  	start
>  	usage
> @@ -16,82 +17,91 @@ KUnit - Unit Testing for the Linux Kernel
>  	tips
>  	running_tips
> 
> -What is KUnit?
> -==============
> -
> -KUnit is a lightweight unit testing and mocking framework for the Linux kernel.
> -
> -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.
> -
> -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.
> -
> -To make running these tests (and reading the results) easier, KUnit offers
> -: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,
> -without requiring a virtual machine or separate hardware.
> -
> -Get started now: Documentation/dev-tools/kunit/start.rst
> -
> -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.
> -
> -KUnit provides a common framework for unit tests within the kernel.
> -
> -KUnit tests can be run on most architectures, and most tests are architecture
> -independent. All built-in KUnit tests run on kernel startup.  Alternatively,
> -KUnit and KUnit tests can be built as modules and tests will run when the test
> -module is loaded.
> -
> -.. note::
> -
> -        KUnit can also run tests without needing a virtual machine or actual
> -        hardware under User Mode Linux. User Mode Linux is a Linux architecture,
> -        like ARM or x86, which compiles the kernel as a Linux executable. KUnit
> -        can be used with UML either by building with ``ARCH=um`` (like any other
> -        architecture), or by using :doc:`kunit_tool <kunit-tool>`.
> -
> -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?
> +This section details the kernel unit testing framework.
> +
> +Introduction
> +============
> +
> +KUnit (Kernel unit testing framework) provides a common framework for
> +unit tests within the Linux kernel. Using KUnit, you can define groups
> +of test cases called test suites. The tests either run on kernel boot
> +if built-in, or load as a module. KUnit automatically flags and reports
> +failed test cases in the kernel log. The test results appear in `TAP
> +(Test Anything Protocol) format <https://testanything.org/>`_. It is inspired by
> +JUnit, Python’s unittest.mock, and GoogleTest/GoogleMock (C++ unit testing
> +framework).
> +
> +KUnit tests are part of the kernel, written in the C (programming)
> +language, and test parts of the Kernel implementation (example: a C
> +language function). Excluding build time, from invocation to
> +completion, KUnit can run around 100 tests in less than 10 seconds.
> +KUnit can test any kernel component, for example: file system, system
> +calls, memory management, device drivers and so on.
> +
> +KUnit follows the white-box testing approach. The test has access to
> +internal system functionality. KUnit runs in kernel space and is not
> +restricted to things exposed to user-space.
> +
> +In addition, KUnit has kunit_tool, a script (``tools/testing/kunit/kunit.py``)
> +that configures the Linux kernel, runs KUnit tests under QEMU or UML (`User Mode
> +Linux <http://user-mode-linux.sourceforge.net/>`_), parses the test results and
> +displays them in a user friendly manner.
> +
> +Features
> +--------
> +
> +- Provides a framework for writing unit tests.
> +- Runs tests on any kernel architecture.
> +- Runs a test in milliseconds.
> +
> +Prerequisites
> +-------------
> +
> +- Any Linux kernel compatible hardware.
> +- For Kernel under test, Linux kernel version 5.5 or greater.
> +
> +Unit Testing
> +============
> +
> +A unit test tests a single unit of code in isolation. A unit test is the finest
> +granularity of testing and allows all possible code paths to be tested in the
> +code under test. This is possible if the code under test is small and does not
> +have any external dependencies outside of the test's control like hardware.
> +
> +
> +Write Unit Tests
> +----------------
> +
> +To write good unit tests, there is a simple but powerful pattern:
> +Arrange-Act-Assert. This is a great way to structure test cases and
> +defines an order of operations.
> +
> +- Arrange inputs and targets: At the start of the test, arrange the data
> +  that allows a function to work. Example: initialize a statement or
> +  object.
> +- Act on the target behavior: Call your function/code under test.
> +- Assert expected outcome: Verify the result (or resulting state) as expected
> +  or not.

Verify the result (or resulting state) as expected or not ->
   Verify that the result (or resulting state) is as expected or not


> +
> +Unit Testing Advantages
> +-----------------------
> +
> +- Increases testing speed and development in the long run.
> +- Detects bugs at initial stage and therefore decreases bug fix cost
> +  compared to acceptance testing.
> +- Improves code quality.
> +- Encourages writing testable code.
> 
>  How do I use it?
>  ================
> 
> -*   Documentation/dev-tools/kunit/start.rst - for new users of KUnit
> -*   Documentation/dev-tools/kunit/tips.rst - for short examples of best practices
> -*   Documentation/dev-tools/kunit/usage.rst - for a more detailed explanation of KUnit features
> -*   Documentation/dev-tools/kunit/api/index.rst - for the list of KUnit APIs used for testing
> -*   Documentation/dev-tools/kunit/kunit-tool.rst - for more information on the kunit_tool helper script
> -*   Documentation/dev-tools/kunit/faq.rst - for answers to some common questions about KUnit
> +*   Documentation/dev-tools/kunit/start.rst - for KUnit new users.
> +*   Documentation/dev-tools/kunit/usage.rst - KUnit features.
> +*   Documentation/dev-tools/kunit/tips.rst - best practices with
> +    examples.
> +*   Documentation/dev-tools/kunit/api/index.rst - KUnit APIs
> +    used for testing.
> +*   Documentation/dev-tools/kunit/kunit-tool.rst - kunit_tool helper
> +    script.
> +*   Documentation/dev-tools/kunit/faq.rst - KUnit common questions and
> +    answers.
> --
> 2.34.1.400.ga245620fadb-goog

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