assert(CW6c.get_prices(List("BIDU"), 2004 to 2008) ==
List(List(None), List(None),
List(Some(6.35)), List(Some(12.241)),
List(Some(38.188))))
assert(CW6c.get_prices(List("GOOG", "AAPL"), 2010 to 2012) ==
List(List(Some(311.349976), Some(27.505054)),
List(Some(300.222351), Some(42.357094)),
List(Some(330.555054), Some(52.852215))))