Join GitHub today
adds tests for the missing members of RTCRtpHeaderExtensionParameters #10282
Sorry, I don't think that this proposal for more tests makes sense.
It's not possible to add RTP extensions that the browser doesn't support - they require code deep in the WebRTC RTP engine, which you can't add through the API.
See http://w3c.github.io/webrtc-pc/#rtcrtpparameters - the header extensions is a read-only parameter.
I don't have any idea how you can verify that these mandatory fields in a read-only parameter are mandatory, but this approach won't work.