ballTest(5, 'xxxxx')); being true bothers me; I think it should be false.
Spec says
'return whether or not the ball will be able to make it past the end of the road'
'The ball must fall off of the edge of the road for the code to be considered valid.'
The speed at the end of the road is -1, the ball is stuck on the 5th crack, never to make it past the end of the road.