--- a/dom/events/test/test_all_synthetic_events.html
+++ b/dom/events/test/test_all_synthetic_events.html
@@ -286,17 +286,20 @@ const kEventConstructors = {
                                              },
   ProgressEvent:                             { create: function (aName, aProps) {
                                                          return new ProgressEvent(aName, aProps);
                                                        },
                                              },
   RTCDataChannelEvent:                       { create: function (aName, aProps) {
                                                          let pc = new RTCPeerConnection();
                                                          aProps.channel = pc.createDataChannel("foo");
-                                                         return new RTCDataChannelEvent(aName, aProps);
+                                                         let e = new RTCDataChannelEvent(aName, aProps);
+                                                         aProps.channel.close();
+                                                         pc.close();
+                                                         return e;
                                                        },
                                              },
   RTCDTMFToneChangeEvent:                       { create: function (aName, aProps) {
                                                          return new RTCDTMFToneChangeEvent(aName, aProps);
                                                        },
                                              },
   RTCPeerConnectionIceEvent:                 { create: function (aName, aProps) {
                                                          return new RTCPeerConnectionIceEvent(aName, aProps);