Re: [RFC v2 00/14] kunit: introduce KUnit, the Linux kernel unit testing framework

From: Daniel Vetter
Date: Wed Oct 24 2018 - 05:14:57 EST

On Tue, Oct 23, 2018 at 04:57:36PM -0700, Brendan Higgins wrote:
> 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.
> ## 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.
> ## 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.
> ## 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:
> ## Changes Since Last Version
> - Updated patchset to apply cleanly on 4.19.
> - Stripped down patchset to focus on just the core features (I dropped
> mocking, spying, and the MMIO stuff for now; you can find these
> patches here:,
> as suggested by Rob.
> - Cleaned up some of the commit messages and tweaked commit order a
> bit based on suggestions.

Do you have some example unit tests somewhere? The docs are all neat, but
real example helps a lot with the tried&true art of copypasting :-)

I'd like to give this a test spin with some of the unit tests we already
have in drm. And especially figuring out how we could integrate this with
our existing infrastructure.
Daniel Vetter
Software Engineer, Intel Corporation