its subjective jon.
there are lots of definitions of solid and you can choose which your preferred one is

a pattern is solid when you can:
jugglie it for x catches
juggle it for y cycles
juggle it from cold
juggle it looking at someone/thing through the pattern
juggle using it as your 'resting' pattern
i usually go by the 'do it from cold' measure and the even more subjective, 'when i feel comfortable with it'.
the best test of if i think have a trick solid is whether or not i will attempt it with globalls in a club

cole. x