Tone.js/test/helper/PassAudio.js

define(["helper/Test", "Tone/core/Offline", "Tone/signal/Signal", "Tone/core/Master"], 
	function(Test, Offline, Signal, Master){

		var PassAudio = function(before){

			var duration = 0.2;
			return Offline(function(){
				var sig = new Signal(0);
				before(sig);
				sig.setValueAtTime(1, duration / 2);
			}, duration).then(function(buffer){
				var array = buffer.toMono().toArray();
				for (var i = 0; i < array.length; i++){
					var time = (i / array.length) * duration;
					var sample = array[i];
					if (time >= duration / 2 && sample !== 0){
						return true;
					} else if (time < duration / 2){
						expect(sample).to.be.closeTo(0, 0.001);
					}
				}
				throw new Error("node outputs silence");
			});
		};

		return PassAudio;
	});