def METHOD_NAME():
    mrp = SubClass4("mrp")
    dmap = SubClass4("dmap")
    airplay = SubClass4("airplay")
    relayer = Relayer(BaseClass, [Protocol.MRP, Protocol.DMAP, Protocol.AirPlay])
    relayer.register(mrp, Protocol.MRP)
    relayer.register(dmap, Protocol.DMAP)
    relayer.register(airplay, Protocol.AirPlay)
    instances = relayer.instances
    assert len(instances) == 3
    assert mrp in instances
    assert dmap in instances
    assert airplay in instances