added unit test for p5.gain in es6

test/test.js

@@ -9,8 +9,8 @@ require.config({
 
 var allTests = [
   'tests/p5.Master',
+  'tests/p5.Gain',
   'tests/p5.SoundFile',
-  'tests/p5.Amplitude',
   'tests/p5.Oscillator',
   'tests/p5.Distortion',
   'tests/p5.Effect',

test/tests/p5.Gain.js

@@ -0,0 +1,51 @@
+'use strict '
+
+define(['chai'],(chai)=>{
+    const expect = chai.expect ;
+    describe('P5.Gain',()=>{
+        it('can be initilized and disposed',()=>{
+            let gain = new p5.Gain();
+            gain.dispose();
+        });
+        it('can set input', ()=>{
+            let inputNode = new p5.Gain();
+            let mainGainNode  = new p5.Gain();
+
+            mainGainNode.setInput(inputNode);
+        });
+        it('can send output',()=>{
+            let outputNode = new p5.Gain();
+            let mainGainNode  = new p5.Gain();
+
+            mainGainNode.connect(outputNode);
+        });
+        it('can disconnect  all output' ,()=>{
+            let inputNode = new p5.Gain();
+            let outputNode = new p5.Gain();
+            let mainGainNode  = new p5.Gain();
+
+            mainGainNode.setInput(inputNode);
+            mainGainNode.connect(outputNode);
+            mainGainNode.disconnect();
+        });
+        it('can set the output level of gain Node', ()=>{
+            let osc = new p5.Oscillator('sine');
+            let mainGainNode  = new p5.Gain();
+            let amplitude = new p5.Amplitude();
+
+            osc.amp(1);
+            osc.start();
+            osc.disconnect();
+
+            mainGainNode.setInput(osc);
+            amplitude.setInput(mainGainNode);
+
+            mainGainNode.amp(0.5);
+            setTimeout(function() {
+                expect( amplitude.getLevel() ).to.be.closeTo(0.25, 0.125);
+              }, 100);
+
+        })
+    });
+
+}) ;