def METHOD_NAME(self):
    tag = mutagen.mp4.MP4(self.f)
    tag["----:com.apple.iTunes:MusicBrainz Release Track Id"] = [b"foo"]
    tag.save()
    song = MP4File(self.f)
    self.assertEqual(song("musicbrainz_releasetrackid"), u"foo")
    song["musicbrainz_releasetrackid"] = u"bla"
    song.write()
    tag = mutagen.mp4.MP4(self.f)
    self.assertEqual(
        tag["----:com.apple.iTunes:MusicBrainz Release Track Id"],
        [b"bla"])