
PASS replaceTrack() sets the track attribute to a new track. 
PASS replaceTrack() sets the track attribute to null. 
PASS replaceTrack() does not set the track synchronously. 
PASS replaceTrack() rejects when the peer connection is closed. 
PASS replaceTrack() does not reject when invoked after removeTrack(). 
PASS replaceTrack() does not reject after a subsequent removeTrack().