stroke-dasharray and stroke-linecap
stroke-linecap of a dashed path is animated within 6s with
repetition using the values round;square;butt.
This is compared with the behaviour of subpath
with a length of stroke-width/50000, this is
approximately zero for normal painting conditions.
If something larger in red gets visible for butt,
an error occured. Red with round or square is
always an error.
Red comparison - if visible - error -
with butt a small red feature with a length
of stroke-width/50000 is ok
Dark gray - unspecified if covered or not
Blue testcase covers all red if correct
Light gray - shows centers of dashes