Bug 1629565: Test that we do not transition to "gathering" on a simple reoffer. r=jib

Differential Revision: https://phabricator.services.mozilla.com/D72236

testing/web-platform/tests/webrtc/RTCPeerConnection-iceGatheringState.html

@@ -84,10 +84,53 @@
       assert_unreached(`Unhandled rejection ${err.name}: ${err.message}`)));
   }, 'iceGatheringState should eventually become complete after setLocalDescription');
 
+  const iceGatheringStateTransitions = async (pc, ...states) => {
+    for (const state of states) {
+      await new Promise((resolve, reject) => {
+        pc.addEventListener('icegatheringstatechange', () => {
+          if (pc.iceGatheringState == state) {
+            resolve();
+          } else {
+            reject(`Unexpected gathering state: ${pc.iceGatheringState}, was expecting ${state}`);
+          }
+        }, {once: true});
+      });
+    }
+  };
+
+  const initialOfferAnswer = async (pc1, pc2, offerOptions) => {
+    await pc1.setLocalDescription(
+      await pc1.createOffer(offerOptions));
+    const pc1Transitions = iceGatheringStateTransitions(pc1, 'gathering', 'complete');
+    await pc2.setRemoteDescription(pc1.localDescription);
+    await pc2.setLocalDescription(await pc2.createAnswer());
+    const pc2Transitions = iceGatheringStateTransitions(pc2, 'gathering', 'complete');
+    await pc1.setRemoteDescription(pc2.localDescription);
+
+    await pc1Transitions;
+    await pc2Transitions;
+  };
+
   const expectNoMoreGatheringStateChanges = async (t, pc) => {
     pc.onicegatheringstatechange = t.step_func(() => assert_unreached('Should not get an icegatheringstatechange right now!'));
   };
 
+  promise_test(async t => {
+    const pc1 = new RTCPeerConnection();
+    t.add_cleanup(() => pc1.close());
+    const pc2 = new RTCPeerConnection();
+    t.add_cleanup(() => pc2.close());
+    await initialOfferAnswer(pc1, pc2, {offerToReceiveAudio:true});
+
+    expectNoMoreGatheringStateChanges(t, pc1);
+    expectNoMoreGatheringStateChanges(t, pc2);
+
+    await pc1.setLocalDescription(await pc1.createOffer());
+    await pc2.setLocalDescription(await pc2.createOffer());
+
+    await new Promise(r => t.step_timeout(r, 500));
+  }, 'setLocalDescription(reoffer) with no new transports should not cause iceGatheringState to change');
+
   promise_test(async t => {
     const pc1 = new RTCPeerConnection();
     t.add_cleanup(() => pc1.close());