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    SubjectRe: [PATCH v2 00/17] kunit: introduce KUnit, the Linux kernel unit testing framework
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    On 5/7/19 1:01 AM, Greg KH wrote:
    > On Mon, May 06, 2019 at 08:14:12PM -0700, Frank Rowand wrote:
    >> 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?
    >
    > kselftest provides no in-kernel framework for testing kernel code
    > specifically. That should be what kunit provides, an "easy" way to
    > write in-kernel tests for things.

    kselftest provides a mechanism for in-kernel tests via modules. For
    example, see:

    tools/testing/selftests/vm/run_vmtests invokes:
    tools/testing/selftests/vm/test_vmalloc.sh
    loads module:
    test_vmalloc
    (which is built from lib/test_vmalloc.c if CONFIG_TEST_VMALLOC)

    A very quick and dirty search (likely to miss some tests) finds modules:

    test_bitmap
    test_bpf
    test_firmware
    test_printf
    test_static_key_base
    test_static_keys
    test_user_copy
    test_vmalloc

    -Frank

    >
    > Brendan, did I get it right?
    >
    > thanks,
    >
    > greg k-h
    > .
    >

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