Tone.js/test/helper/Offline.js

define(["Tone/core/Tone", "Tone/core/Offline", "helper/BufferTest", "Tone/core/Master"], 
	function (Tone, Offline, BufferTest, Master) {

		return function(callback, duration, channels){
			duration = duration || 0.1;
			channels = channels || 1;
			return Offline(function(Transport){
				var testFn = callback(Transport);
				if (testFn){
					Transport.context.on("tick", function(){
						testFn(Transport.now());
					});
				}
			}, duration).then(function(buffer){
				BufferTest(buffer);
				if (channels === 1){
					buffer.toMono();
				}
				return buffer;
			});
		};
	});