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    SubjectRe: [PATCH v2 00/17] kunit: introduce KUnit, the Linux kernel unit testing framework
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    On 5/1/19 4:01 PM, Brendan Higgins wrote:
    > ## TLDR
    >
    > I rebased the last patchset on 5.1-rc7 in hopes that we can get this in
    > 5.2.
    >
    > Shuah, I think you, Greg KH, and myself talked off thread, and we agreed
    > we would merge through your tree when the time came? Am I remembering
    > correctly?
    >
    > ## Background
    >
    > This patch set proposes KUnit, a lightweight unit testing and mocking
    > framework for the Linux kernel.
    >
    > Unlike Autotest and kselftest, KUnit is a true unit testing framework;
    > it does not require installing the kernel on a test machine or in a VM
    > and does not require tests to be written in userspace running on a host
    > kernel. Additionally, KUnit is fast: From invocation to completion KUnit
    > can run several dozen tests in under a second. Currently, the entire
    > KUnit test suite for KUnit runs in under a second from the initial
    > invocation (build time excluded).
    >
    > 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, mocking, spying, and much more.

    As a result of the emails replying to this patch thread, I am now
    starting to look at kselftest. My level of understanding is based
    on some slide presentations, an LWN article, https://kselftest.wiki.kernel.org/
    and a _tiny_ bit of looking at kselftest code.

    tl;dr; I don't really understand kselftest yet.


    (1) why KUnit exists

    > ## What's so special about unit testing?
    >
    > A unit test is supposed to test a single unit of code in isolation,
    > hence the name. There should be no dependencies outside the control of
    > the test; this means no external dependencies, which makes tests orders
    > of magnitudes faster. Likewise, since there are no external dependencies,
    > there are no hoops to jump through to run the tests. Additionally, this
    > makes unit tests deterministic: a failing unit test always indicates a
    > problem. Finally, because unit tests necessarily have finer granularity,
    > they are able to test all code paths easily solving the classic problem
    > of difficulty in exercising error handling code.

    (2) KUnit is not meant to replace kselftest

    > ## Is KUnit trying to replace other testing frameworks for the kernel?
    >
    > No. Most existing tests for the Linux kernel are end-to-end tests, which
    > have their place. A well tested system has lots of unit tests, a
    > reasonable number of integration tests, and some end-to-end tests. KUnit
    > is just trying to address the unit test space which is currently not
    > being addressed.

    My understanding is that the intent of KUnit is to avoid booting a kernel on
    real hardware or in a virtual machine. That seems to be a matter of semantics
    to me because isn't invoking a UML Linux just running the Linux kernel in
    a different form of virtualization?

    So I do not understand why KUnit is an improvement over kselftest.

    It seems to me that KUnit is just another piece of infrastructure that I
    am going to have to be familiar with as a kernel developer. More overhead,
    more information to stuff into my tiny little brain.

    I would guess that some developers will focus on just one of the two test
    environments (and some will focus on both), splitting the development
    resources instead of pooling them on a common infrastructure.

    What am I missing?

    -Frank


    >
    > ## More information on KUnit
    >
    > There is a bunch of documentation near the end of this patch set that
    > describes how to use KUnit and best practices for writing unit tests.
    > For convenience I am hosting the compiled docs here:
    > https://google.github.io/kunit-docs/third_party/kernel/docs/
    > Additionally for convenience, I have applied these patches to a branch:
    > https://kunit.googlesource.com/linux/+/kunit/rfc/v5.1-rc7/v1
    > The repo may be cloned with:
    > git clone https://kunit.googlesource.com/linux
    > This patchset is on the kunit/rfc/v5.1-rc7/v1 branch.
    >
    > ## Changes Since Last Version
    >
    > None. I just rebased the last patchset on v5.1-rc7.
    >

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