First thing is to make creating test layouts easier. Create several scenarios in which all items should be removed from the screen and the item generator. The UI test can shoot at an item that will set off a chain of events and clear all the items on the screen. The test can just check to make sure all child node items have been removed from the parent, the number of balls hasn't changed, and that the item generator is empty.
The second idea is to test the game under intense lag. This helps uncover some weird timing issues. One example is that at the end of a level, the animation fading in the special background doesn't wait for the overlay saying you passed the level. Another example is that under intense lag, a random ball will fire off in a random direction and slowly while the rest of the balls maintain their correct course and speed. And a third example is that the balls won't all get to the origin point before the turn is marked "over" and the items shift down and the items all stop.
2 ideas for testing: