I define a test piece as a difficult route for the grade. It has to Test the leader. It can test the actually climbing skills being a very technical climb, it can very physical or it can be a mental route, preferably it is all three.
Lava Falls, is heady for 5.9 with a bit of a run through the bulge. It is also physical since it is a bit steep. For 5.9 good skills are needed for the upper bulge.
Nexus, heady and skills not real physical since you can get a good rest below and in the crux.
Gorillas in the Moss, skills and physical.