tests: test posting errors
tests: test posting errors

Test posting errors to one and more clients.

Reviewed-by: Pekka Paalanen <0f6ae7001e34c37b02fb2c1c2573ddf8f442136a@collabora.co.uk>

mchalupa/wayland,bitfactor/wayland,bitfactor/wayland,tulcod/wayland,sir-murray/wayland,sir-murray/wayland,eyolfson/wayland,sir-murray/wayland,eyolfson/wayland,mchalupa/wayland,bitfactor/wayland,abooij/wayland,tulcod/wayland,tulcod/wayland,abooij/wayland,abooij/wayland,mchalupa/wayland,eyolfson/wayland