mozilla-release/testing/web-platform/tests/webrtc/RTCPeerConnection-setRemoteDescription-simulcast.https.html

<!doctype html>
<meta charset=utf-8>
<title>RTCPeerConnection.prototype.setRemoteDescription rollback</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="RTCPeerConnection-helper.js"></script>
<script>
'use strict';
// Test for https://github.com/w3c/webrtc-pc/pull/2155
promise_test(async t => {
  const pc = new RTCPeerConnection();
  t.add_cleanup(() => pc.close());
  const [track, stream] = await getTrackFromUserMedia('video');
  t.add_cleanup(() => track.stop());

  pc.addTrack(track, stream);

  const offer_sdp = `v=0
o=- 3840232462471583827 2 IN IP4 127.0.0.1
s=-
t=0 0
a=group:BUNDLE 0
a=msid-semantic: WMS
m=video 9 UDP/TLS/RTP/SAVPF 96
c=IN IP4 0.0.0.0
a=rtcp:9 IN IP4 0.0.0.0
a=ice-ufrag:Li6+
a=ice-pwd:3C05CTZBRQVmGCAq7hVasHlT
a=ice-options:trickle
a=fingerprint:sha-256 5B:D3:8E:66:0E:7D:D3:F3:8E:E6:80:28:19:FC:55:AD:58:5D:B9:3D:A8:DE:45:4A:E7:87:02:F8:3C:0B:3B:B3
a=setup:actpass
a=mid:0
a=extmap:4 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=recvonly
a=rtcp-mux
a=rtpmap:96 VP8/90000
a=rtcp-fb:96 goog-remb
a=rtcp-fb:96 transport-cc
a=rtcp-fb:96 ccm fir
a=rid:foo recv
a=rid:bar recv
a=rid:baz recv
a=simulcast:recv foo;bar;baz
`;

  await pc.setRemoteDescription({type: 'offer', sdp: offer_sdp});
  const transceivers = pc.getTransceivers();
  assert_equals(transceivers.length, 1, 'Expected exactly one transceiver');
}, 'createAnswer() attaches to an existing transceiver with a remote simulcast offer');
</script>