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