def myassert(cond : => Boolean) = {
  try {
    assert(cond)
  } catch { 
    case _ : Throwable => System.exit(1)
  }
}

myassert(get_prices(List("BIDU"), 2004 to 2008) ==
   List(List(None), List(None), List(Some(6.35)), 
        List(Some(12.241)), List(Some(38.188))))


myassert(get_prices(List("GOOG", "AAPL"), 2010 to 2012) ==
   List(List(Some(312.204773), Some(26.782711)), 
        List(Some(301.0466), Some(41.244694)), 
        List(Some(331.462585), Some(51.464207))))