VA-API is an API for video/image decoding/encoding acceleration implemented by libva (x11-libs/libva). libva-fake-driver provides a fake backend for it for VMs and other test-related images.
It can be explicitly exercised by running e.g.:
LIBVA_DRIVER_NAME="fake" vainfo
wherever it might be installed. See https://tinyurl.com/libva-fake-driver for more information.