Due to its nature, the display stack can be hard to test. Indeed, the component we want to test often sends the pixels to an external display without any way to retrieve the image being output, let alone make sure it's correct.
And while a human can perform some of those tests by looking at the screen, some issues can prove to be difficult to spot, such as colours being slightly off or pixels being offset. More complex tests can also be tedious to set up or hard to trigger.
The ecosystem of devices that Linux supports also adds further constraints on the display interfaces we want to test, but also on the system size, the tools available, the connectivity of the device, etc.
In this talk, we will first discuss the constraints and what makes testing the display stack unique. We will then talk about the existing solutions, their limitations, and what we have been working on to improve the situation.