Unit tests, originally for KVM, but also expanding to cover QEMU TCG mode, and potentially useful elsewhere. The unit tests are tiny guest operating systems that generally execute only tens of lines of C and assembler test code in order to obtain its PASS/FAIL result. The tests provide KVM and virt hardware functional testing by targeting the features through minimal implementations of their use per the hardware specification. The simplicity of unit tests make them easy to verify they are correct, easy to maintain, and easy to use in timing measurements. Unit tests are also often used for quick and dirty bug reproducers. The reproducers may then be kept as regression tests. It's strongly encouraged that patches implementing new KVM features are submitted with accompanying unit tests.
These details are provided for information only. No information here is legal advice and should not be used as such.