fix tests

packages/webaudio/feedbackdelay.mjs

@@ -1,4 +1,5 @@
-class FeedbackDelayNode extends DelayNode {
+if (typeof DelayNode !== 'undefined') {
+  class FeedbackDelayNode extends DelayNode {
     constructor(ac, wet, time, feedback) {
       super(ac);
       wet = Math.abs(wet);
@@ -21,8 +22,9 @@ class FeedbackDelayNode extends DelayNode {
     start(t) {
       this.delayGain.gain.setValueAtTime(this.delayGain.gain.value, t + this.delayTime.value);
     }
-}
+  }
 
-AudioContext.prototype.createFeedbackDelay = function (wet, time, feedback) {
+  AudioContext.prototype.createFeedbackDelay = function (wet, time, feedback) {
     return new FeedbackDelayNode(this, wet, time, feedback);
-};
+  };
+}