1.. SPDX-License-Identifier: GPL-2.0
2
3==========================
4Frequently Asked Questions
5==========================
6
7How is this different from Autotest, kselftest, and so on?
8==========================================================
9KUnit is a unit testing framework. Autotest, kselftest (and some others) are
10not.
11
12A `unit test <https://martinfowler.com/bliki/UnitTest.html>`_ is supposed to
13test a single unit of code in isolation and hence the name *unit test*. A unit
14test should be the finest granularity of testing and should allow all possible
15code paths to be tested in the code under test. This is only possible if the
16code under test is small and does not have any external dependencies outside of
17the test's control like hardware.
18
19There are no testing frameworks currently available for the kernel that do not
20require installing the kernel on a test machine or in a virtual machine. All
21testing frameworks require tests to be written in userspace and run on the
22kernel under test. This is true for Autotest, kselftest, and some others,
23disqualifying any of them from being considered unit testing frameworks.
24
25Does KUnit support running on architectures other than UML?
26===========================================================
27
28Yes, mostly.
29
30For the most part, the KUnit core framework (what we use to write the tests)
31can compile to any architecture. It compiles like just another part of the
32kernel and runs when the kernel boots, or when built as a module, when the
33module is loaded.  However, there is infrastructure, like the KUnit Wrapper
34(``tools/testing/kunit/kunit.py``) that does not support other architectures.
35
36In short, yes, you can run KUnit on other architectures, but it might require
37more work than using KUnit on UML.
38
39For more information, see :ref:`kunit-on-non-uml`.
40
41What is the difference between a unit test and other kinds of tests?
42====================================================================
43Most existing tests for the Linux kernel would be categorized as an integration
44test, or an end-to-end test.
45
46- A unit test is supposed to test a single unit of code in isolation. A unit
47  test should be the finest granularity of testing and, as such, allows all
48  possible code paths to be tested in the code under test. This is only possible
49  if the code under test is small and does not have any external dependencies
50  outside of the test's control like hardware.
51- An integration test tests the interaction between a minimal set of components,
52  usually just two or three. For example, someone might write an integration
53  test to test the interaction between a driver and a piece of hardware, or to
54  test the interaction between the userspace libraries the kernel provides and
55  the kernel itself. However, one of these tests would probably not test the
56  entire kernel along with hardware interactions and interactions with the
57  userspace.
58- An end-to-end test usually tests the entire system from the perspective of the
59  code under test. For example, someone might write an end-to-end test for the
60  kernel by installing a production configuration of the kernel on production
61  hardware with a production userspace and then trying to exercise some behavior
62  that depends on interactions between the hardware, the kernel, and userspace.
63
64KUnit is not working, what should I do?
65=======================================
66
67Unfortunately, there are a number of things which can break, but here are some
68things to try.
69
701. Run ``./tools/testing/kunit/kunit.py run`` with the ``--raw_output``
71   parameter. This might show details or error messages hidden by the kunit_tool
72   parser.
732. Instead of running ``kunit.py run``, try running ``kunit.py config``,
74   ``kunit.py build``, and ``kunit.py exec`` independently. This can help track
75   down where an issue is occurring. (If you think the parser is at fault, you
76   can run it manually against ``stdin`` or a file with ``kunit.py parse``.)
773. Running the UML kernel directly can often reveal issues or error messages,
78   ``kunit_tool`` ignores. This should be as simple as running ``./vmlinux``
79   after building the UML kernel (for example, by using ``kunit.py build``).
80   Note that UML has some unusual requirements (such as the host having a tmpfs
81   filesystem mounted), and has had issues in the past when built statically and
82   the host has KASLR enabled. (On older host kernels, you may need to run
83   ``setarch `uname -m` -R ./vmlinux`` to disable KASLR.)
844. Make sure the kernel .config has ``CONFIG_KUNIT=y`` and at least one test
85   (e.g. ``CONFIG_KUNIT_EXAMPLE_TEST=y``). kunit_tool will keep its .config
86   around, so you can see what config was used after running ``kunit.py run``.
87   It also preserves any config changes you might make, so you can
88   enable/disable things with ``make ARCH=um menuconfig`` or similar, and then
89   re-run kunit_tool.
905. Try to run ``make ARCH=um defconfig`` before running ``kunit.py run``. This
91   may help clean up any residual config items which could be causing problems.
926. Finally, try running KUnit outside UML. KUnit and KUnit tests can be
93   built into any kernel, or can be built as a module and loaded at runtime.
94   Doing so should allow you to determine if UML is causing the issue you're
95   seeing. When tests are built-in, they will execute when the kernel boots, and
96   modules will automatically execute associated tests when loaded. Test results
97   can be collected from ``/sys/kernel/debug/kunit/<test suite>/results``, and
98   can be parsed with ``kunit.py parse``. For more details, see "KUnit on
99   non-UML architectures" in Documentation/dev-tools/kunit/usage.rst.
100
101If none of the above tricks help, you are always welcome to email any issues to
102kunit-dev@googlegroups.com.
103