Refactor percussion tests (#497)
Refactor percussion tests (#497)


Silverwolf90/vexflow,Huji/vexflow,Silverwolf90/vexflow,aaronmars/vexflow,Silverwolf90/vexflow,Huji/vexflow,Huji/vexflow,aaronmars/vexflow,aaronmars/vexflow,Tails/vexflow,Tails/vexflow,Tails/vexflow