Test gradient stop rules. Including: No stops, like fill = none. One stop, like fill = black. If a stop less than
all previous stops, it is set equal to the largest stop. If two stops are equal the last stop controls the color
at the overlap point.
The top rectangle must have a red outline and no fill. The middle rectangle must have a solid black fill. The
lower rectangle must have a yellow to red to green linear gradient on the left-hand half and a solid blue fill
for the right hand half.
