On 5/1/19 4:01 PM, Brendan Higgins wrote:
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
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
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
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?
## 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:
Additionally for convenience, I have applied these patches to a branch:
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.