1.. SPDX-License-Identifier: GPL-2.0
2
3==========================
4Frequently Asked Questions
5==========================
6
7How is this different from Autotest, kselftest, etc?
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, hence the name. A unit test should be
14the finest granularity of testing and as such should allow all possible code
15paths to be tested in the code under test; this is only possible if the code
16under test is very 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 VM and all require
21tests to be written in userspace and run on the kernel under test; this is true
22for Autotest, kselftest, and some others, disqualifying any of them from being
23considered unit testing frameworks.
24
25Does KUnit support running on architectures other than UML?
26===========================================================
27
28Yes, well, mostly.
29
30For the most part, the KUnit core framework (what you 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. However, there is some infrastructure,
33like the KUnit Wrapper (``tools/testing/kunit/kunit.py``) that does not support
34other architectures.
35
36In short, this means that, yes, you can run KUnit on other architectures, but
37it might require more 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 these 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, hence the
47  name. A unit test should be the finest granularity of testing and as such
48  should allow all possible code paths to be tested in the code under test; this
49  is only possible if the code under test is very small and does not have any
50  external dependencies 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