Earlier today I shared a spot the difference for kwin_wayland with no screenshot attached. The difference was the introduction of a virtual framebuffer backend. This might sound surprising: why would one need it and why would one add it?

The reason to implement it is to be able to run integration tests against KWin. This is something I had "dreamed" about for years, but I never found a solution which satisfied me (Xvfb is extremely limited). With the virtual KWin rendering backend this is finally solved. I just pushed the first simple test case which starts a full KWin, can create Wayland clients and then introspect whether KWin functioned as expected. This is a huge and very important achievement. Unit testing KWin is almost impossible and that at least gives us integration testing.

But this is only the start. I hope we will be able to use it for more. Imagine starting a plasmashell in a virtual KWin, simulating input events, taking screenshots to compare against reference setups.