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
>> 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
>> ## 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
(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: