Removed useless condition in Worker.py that was allowing misfit non-serialized call when worker still not running its loop.
#!/bin/sh
LC_ALL=ru_RU.utf-8
export DISPLAY=:42
Xvfb $DISPLAY -screen 0 1280x1024x24 &
sleep 1
ret=0
DELAY=400
KILL_DELAY=$(($DELAY + 30))
timeout -k $KILL_DELAY $DELAY pytest --timeout=10 ./tests/tools
ret=$?
pkill -9 Xvfb
exit $ret