stroke of a subpath with zero length
Three paths containing a subpath with length zero
or animated to zero are animated.
The paths have stroke-linecap square.
An underlying red path simulates the behaviour using a
subpath with a length very small compared to the stroke-width.
If something red gets visible, an error is occured.
Red comparison - if visible - error
Blue testcase covers all red if correct
Red comparison - if visible - error
Blue testcase covers all red if correct
Red comparison - if visible - error
Blue testcase covers all red if correct