When is a noodle finished cooking
I have heard about throwing it at the ceiling too, but not sure how that is supposed to work. It sounds a little bit too objective as a yes/no answer to "is it a good noodle?" Different people have slightly different ideas how well done they want their noodles. 
Simple to determine experimentally how long is perfect. As the noodles cook, just pull one out of the boiling water at frequent intervals and sample it. Be prepared to quickly drain the water off when the sample noodle reaches the level of doneness that you want. As soon as the noodles get to that point, act.  Drain off the water immediately, voila.